Alabama's state emergency management agency said it had confirmed 128 deaths, up from at least 61 earlier.
"We hope not, but I do expect to find more [bodies]," Gov. Robert Bentley told NBC's TODAY.
Mississippi officials reported 32 dead in that state and Tennessee raised its report to 14. Another 12 have been killed in Georgia and eight in Virginia. In Louisiana, two people drowned.
The fierce storms Wednesday spawned tornadoes and winds that wiped out homes and businesses, forced a nuclear power plant to use backup generators and prompted the evacuation of a National Weather Service office.
The weather system spread destruction from Texas to New York, where dozens of roads were flooded or washed out.
The severe weather was continuing Thursday. The National Weather Service was issuing short-lived tornado warnings — advising people to "take cover now" — as the twisters formed.
Video: Massive twister caught on cameraBy early Thursday, these had been sent out for parts of New York, Maryland, Virginia, North Carolina, South Carolina, Georgia, and Florida.
The NWS Storm Prediction Center in Norman, Okla., said it received 137 tornado reports around the region, including 66 in Alabama and 38 in Mississippi.
The NWS also issued flash flood warnings for parts of New York, Pennsylvania, Missouri, Maryland, Virginia, West Virginia, Arkansas and Georgia, for Thursday morning.
And it further warned of severe thunderstorms in parts of Pennsylvania, New York, Vermont, South Carolina, North Carolina, Virginia and Georgia.
Get the latest updates on the tornadoes at breakingnews.comThe states where fatalities were reported were:
Alabama, where 128 people died and officials said damage was spread over a wide area. "It looks like somebody came through with a huge ax and cut the top off of everything. Just a big blade through that whole area. That area is just total devastation," Tuscaloosa resident David Ikard was quoted as saying by Alabama Live.Mississippi, where 32 were killed, including police officer Wade Sharp who died when a tree fell on his tent as he shielded his young daughter, a ranger with the National Park Service said. The 9-year-old was brought to a motorhome about 100 feet away where campsite volunteer Greg Maier was staying with his wife. Maier went back to check on the father and found him dead. "She wasn't hurt, just scared and soaking wet," he said.
Georgia, where NBC News reported 12 deaths; Gov. Nathan Deal declared a state of emergency in Catoosa, Floyd, Dade and Walker counties.
Louisiana, which was also hit by thunderstorms with high winds and possible tornadoes. Police said they believed two people found dead in Monroe had drowned during heavy flooding Wednesday.
Tennessee, where 14 people were killed. The Hamilton County Sheriff's Office identified one victim as 41-year-old Mai Crumley, of Chattanooga, who died Wednesday when a tree fell on her trailer.
Virginia, where the toll increased from one to eight with officials saying seven more were killed when a possible tornado hit a truck stop and several mobile homes.
The number of deaths was expected to rise with authorities still searching for missing people, NBC News said.
The Weather Channel said the deadliest known tornado outbreak happened in 1925, when 747 people were killed in the infamous Tri-State tornado. In 1974, 307 people were killed. Other notable outbreaks happened in 2008 (57 dead), 1999 (47), 1985 (76) and 1984 (57).
'Awful, terrible, disturbing'
"An awful, terrible, disturbing and deadly day of tornadoes unfolded on Wednesday, April 27, 2011 with more than 100 reported tornadoes striking several states in the South and even a few areas in the Mid-Atlantic," the Weather Channel said in an article written by three of its meteorologists.
Tuscaloosa, a city of more than 83,000 and home to the University of Alabama, was one of the hardest-hit areas.
Video: Alabama governor: More tornado fatalities expected (on this page)The city's police and other emergency services were devastated, the mayor said, and at least 15 people were killed and about 100 were in a single hospital.
A massive tornado barreled through the city late Wednesday afternoon, leveling it.
Video taken at the university showed a massive funnel cloud (on this page) , flinging huge pieces of debris through the air.
A Tuscaloosa resident, Phil Owen, said only one store was left standing at a shopping center. "Big Lots, Full Moon Barbecue ... piles of garbage where those places were," he said. "Shell gas station across the street — all that's standing is the frame of the store."
By nightfall, the city was dark. Roads were impassable. Signs were blown down in front of restaurants, businesses were unrecognizable and sirens wailed off and on. Debris littered the streets and sidewalks.
College students in a commercial district near campus used flashlights to check out the damage.
At Stephanie's Flowers, owner Bronson Englebert used the headlights from two delivery vans to see what valuables he could remove.
He had closed early, which was a good thing. The storm blew out the front of his store, pulled down the ceiling and shattered the windows, leaving only the curtains flapping in the breeze.
"It even blew out the back wall, and I've got bricks on top of two delivery vans now," Englebert said.
'Please pray for us'
A group of students stopped to help Englebert, carrying out items like computers and printers and putting them in his van.
"They've been awfully good to me so far," Englebert said.
"Please pray for us," Tuscaloosa Mayor Walter Maddox said on The Weather Channel as crews fanned out to search for victims in the city of nearly 100,000.
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President Barack Obama said he had spoken with Alabama Gov. Robert Bentley and approved his request for emergency federal assistance, including search and rescue assets. About 1,400 National Guard soldiers were being deployed around the state.
"Our hearts go out to all those who have been affected by this devastation, and we commend the heroic efforts of those who have been working tirelessly to respond to this disaster," Obama said in a statement.
Around Tuscaloosa, traffic was snarled by downed trees and power lines, and some drivers abandoned their cars in medians.
"What we faced today was massive damage on a scale we have not seen in Tuscaloosa in quite some time," Mayor Walter Maddox said.
University officials said there didn't appear to be significant damage on campus, and dozens of students and locals were staying at a 125-bed shelter in the campus recreation center.
Volunteers and staff were providing food and water to people like 29-year-old civil engineering graduate student Kenyona Pierce.
"I really don't know if I have a home to go to," she said.
Storms also struck Birmingham, felling numerous trees that impeded emergency responders and those trying to leave hard-hit areas.
Surrounding Jefferson County reported 11 deaths; another hard-hit area was Walker County in the far northwest part of the state with at least eight deaths. The rest of the deaths were scattered around northern Alabama.
Video: Twister rips through Mississippi scrap yard
Nuke plant emergency event
The Browns Ferry nuclear power plant about 30 miles west of Huntsville lost offsite power. The Tennessee Valley Authority-owned plant had to use seven diesel generators to power the plant's three units.
The safety systems operated as needed and the emergency event was classified as the lowest of four levels, the Nuclear Regulatory Commission said.
In Huntsville, meteorologists found themselves in the path of severe storms and had to take shelter in a reinforced steel room, turning over monitoring duties to a sister office in Jackson, Miss.
Meteorologists saw multiple wall clouds, which sometimes spawn tornadoes, and decided to take cover, but the building wasn't damaged.
"We have to take shelter just like the rest of the people," said meteorologist Chelly Amin, who wasn't at the office at the time but spoke with colleagues about the situation.
She said the extent of the damage statewide is still unknown.
"I really think with the rising of the sun, we'll see the full extent of this," she said.
In Kemper County, Miss., in the east-central part of the state, sisters Florrie Green and Maxine McDonald, and their sister-in-law Johnnie Green, all died in a mobile home that was destroyed by a storm.
Johnnie Green's daughter-in-law said Florrie Green and McDonald owned mobile homes side-by-side, and Johnnie Green lived nearby. Johnnie Green was at one of the woman's homes at the time the storm hit.
"It's hard. It's been very difficult," Mary Green said. "They were thrown into those pines over there," she said, pointing to a wooded area. "They had to go look for their bodies."
Top stories Severe alerts Current snow coverage Airport delays Rush hour trafficIn a neighborhood south of Birmingham, Austin Ransdell and a friend had to hike out after the house where he was living was crushed by four trees. No one was hurt.
As he walked away from the wreckage, trees and power lines crisscrossed residential streets, and police cars and utility trucks blocked a main highway.
"The house was destroyed. We couldn't stay in it. Water pipes broke; it was flooding the basement," he said. "We had people coming in telling us another storm was coming in about four or five hours, so we just packed up."
Not far away, Craig Branch was stunned by the damage.
"Every street to get into our general subdivision was blocked off. Power lines are down; trees are all over the road. I've never seen anything like that before," he said.
In eastern Tennessee, a woman was killed by falling trees in her trailer in Chattanooga. Just outside the city in Tiftonia, what appeared to be a tornado also struck at the base of the tourist peak Lookout Mountain.
Tops were snapped off trees and insulation and metal roof panels littered the ground. Police officers walked down the street, spray-painting symbols on houses they had checked for people who might be inside.
Mary Ann Bowman, 42, stood watching from her driveway as huge tractors moved downed trees in the street. She had rushed home from work to find windows shattered at her house, and her grandmother's house next door shredded. The 91-year-old woman wasn't home at the time.
"When I pulled up I just started crying," Bowman said.
This article contains reporting from The Associated Press, Reuters, NBC News and msnbc.com.
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