Hundreds of gorse fires that have been raging across Northern Ireland since the weekend have been started deliberately according to the Northern Ireland Fire Service.
Elsewhere on the island, fires have been raging in counties including Donegal, Louth and Offaly, this after a prolonged absence of rain and the warmest April on record.
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.
"It is phenomenally busy, it is unbelievable," said Chief Fire Officer Peter Craig.
"Last night (Sunday) on our command board, every light for every station in Northern Ireland was lit, bar one or two."
The largest fire is in the Mourne Mountains in County Down. The smoke from the fire could be seen as far away as Belfast, a distance of about 25 miles at the closest points of both. Mr. Craig said six engines were in the Mourne Mountains trying to deal with gorse fires there.
Police have said that people's lives have been put in danger, hundreds of acres of land destroyed and homes and livestock threatened in the fires.
Police said they were investigating reports of arsonists at work in Rostrevor and Slievegullion Mountain. Police are questioning two boys, aged 10 and 15, in connection with one fire at Sixmilecross, County Tyrone.
The Northern Ireland Fire and Rescue Service said Sunday was one of the busiest days in their history as crews from nearly all of the North's 68 fire stations tackled blazes. That evening, the fire service was getting a call every 45seconds.
Mr. Craig said they have been tackling 40 foot flames that move "faster than people can run."
People have been warned to stay away from the Mournes. Craig said the people behind the fires 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."
Meanwhile, in the Republic, large areas of midland bogland and state forest land have been shrouded in smoke as fires continued to burn and smolder.
A primary reason for the fires, apart from suspected arson in the North, has been the fact that April was the sunniest and the warmest on record across much of Ireland, with temperatures on average three degrees Celsius above normal for the time of year. Meanwhile, rainfall levels were below normal for the month in most areas.