There were gorse fires across NI over the bank holiday weekend - at one stage an average of one call every 45 seconds was being received.
The worst of the blazes on Tuesday is at Glenshesk near Ballycastle.
The Mournes and Gortin were also badly affected, although the flames there have now subsided.
BBC NI reporter Alexandra McKenzie was in Ballycastle on Tuesday afternoon. She said that although fears the fire would spread to the Ballypatrick forest have not been realised, damage was nonetheless extensive.
"The fire has wiped out hundreds of acres of farmland. That will take years before it can be used again," she said.
"There are points when you drive along that you can hardly see in front of your car, you can hardly see where you're going the smoke is so thick.
"It's even difficult to breathe."
Two boys, aged 10 and 15, have been questioned by police about a gorse fire in County Tyrone.
They said they were also following up reports that a man with a petrol can was seen in the Rostrevor area on Saturday evening and that two youths were spotted lighting fires on Slieve Gullion Mountain in south Armagh on Sunday night.
Assistant Chief Constable Gary White said the thought that "individuals may be deliberately causing such destruction is very hard to comprehend".
"Not only are they putting livestock in danger, and destroying the habitat of wildlife, but as seen in the necessary evacuations in Annalong and the Lenamore Road in Omagh, homes and therefore the lives of residents are being threatened," he said.
"I would also appeal to those people who are causing the fires to think of their actions and the consequences involved which will most certainly include prosecution."
A fire on the Munie road in Ballymena on Friday is also believed to have been started deliberately. Police said it claimed around 40 acres of land and, at one stage, threatened to destroy a farm house and out buildings.
'Community problem'Northern Ireland Fire and Rescue Service Chief Fire Officer Peter Craig said it had been "phenomenally busy".
"What we are highly concerned with is protecting life, property and infrastructure," he said.
"In Rostrevor, I saw a ball of flames rolling towards a property. Firefighters, the local community and property owners themselves worked extremely hard to make sure that that person's home did not go up in flames."
Mr Craig said this was a "community problem" and adults should question young people about where they are going.
"Not only are they putting the community at risk, they are putting themselves at risk," he said.
The NIFRS said the holiday weekend had been the busiest in its history.
In a 24-hour period from midday on Sunday, the fire service received 927 calls and sent appliances to a total of 376 incidents. Gorse and grassland fires accounted for 194 of these.
