The worst are in the Mourne Mountains where crews continue to tackle blazes with flames as high as 40 ft. People have been urged to stay away, as it is very dangerous.
In Omagh, families had to flee their homes overnight because of a fire.
Most of the gorse fires are believed to have been started deliberately.
The NI Fire and Rescue Service said their resources were under strain.
Chief Fire Officer Peter Craig said they have been tackling 40ft flames that move "faster than people can run" in the Mourne Mountains.
The National Trust has warned that the fires will cause "immense damage" to the area.
The fire service said the blaze in the Mournes was one of the "most significant for many years".
It warned it did not have enough resources to put it out and maintain an acceptable level of cover elsewhere.
Firefighters from 60 of Northern Ireland's 68 stations attended the scene in the Mournes, along with other gorse fires in Tyrone, Fermanagh, Divis Mountain in Belfast and at the Glenshane Pass.
Ten fire appliances alone were called to a blaze in Rostrevor.
A number of roads in the Rostrevor, Hilltown and Kilbroney areas of south County Down were closed.'At risk'
Mr Craig believes the vast majority of the fires have been started deliberately.
He said the people behind them were putting lives at risk.
"The key issue is they need to know their actions have consequences," he said.
"People out in the mountains enjoying the day are coming down facing a ferocious fire. One moment of what they consider fun could end in a tragedy.
"Somebody could lose their life."
In County Antrim, on the Cushendall Road, two miles from Ballycastle, police issued a warning on Sunday after a gorse fire made driving conditions extremely dangerous.
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