The number of blazes in Indonesia’s rain forests has jumped sharply, satellite data showed Thursday, spreading smog across South-East Asia and adding to concerns about the impact of increasing wildfire outbreaks worldwide on global warming.

Illegal blazes to clear land for agricultural plantations have been raging on Sumatra and Borneo islands, with Indonesia deploying water-bombing helicopters and thousands of security forces to tackle them.

It is just the latest such outbreak worldwide – huge blazes have torn through the Amazon in South America while bush fires are sweeping across eastern Australia in an unusually ferocious and early start to the wildfire season.

Indonesia’s forest fires are an annual problem but have been worsened this year by particularly dry weather, and in recent days sent toxic smog floating over Malaysia and triggered a diplomatic row.

There were 1,619 hotspots detected on the Indonesian part of Borneo and Sumatra up from 861 a day earlier, according to a tally from the center, which monitors forest fires and smog outbreaks.