JAKARTA (REUTERS) - Indonesia's western province of Riau has declared a state of emergency over forest and land fires blazing on the island of Sumatra, a government official said on Tuesday (March 9).

The fires, which send choking smog over South-east Asia every year, raged uncontrollably across several provinces last year, costing an estimated US$16 billion (S$22 billion), and pushed average daily greenhouse gas emissions above those of the United States.

"The governor has declared an emergency now, to be able to prevent a repeat of the haze that occurred in 2015," said provincial government spokesman Darusman, adding that life in the province continued to be normal.

About 500 military and police personnel and a water-bombing helicopter have been deployed to help fight the fires but the haze had not yet reached urban areas, he said.

The fires are often set by plantation companies and smallholders to clear land, and were particularly bad in 2015 because of a prolonged dry season caused by the El Nino weather pattern.

Indonesian President Joko Widodo has urged authorities to contain so-called hot spots, where fires start and spread to their surroundings.

This year, Mr Joko set up an agency to restore around 2 million ha of carbon-rich peatlands which typically produce more smog than forest fires.

But past efforts by Indonesia and neighbouring countries to prevent the fires, or put them out once started, have shown little success. Last year's fires ended only when the rainy season arrived to douse them.