Forest fires have been detected in at least five districts in Riau province on Sumatra island, said Sutopo Nugroho, spokesman for the National Disaster Management Agency.
"Fires are on the rise in Riau," he said, adding that they were the cause of Singapore's haze.
The Straits Times newspaper reported that as of 5 pm Friday, Singapore's 24-hour Pollutant Standard Index stood in the unhealthy range.
Six Indonesian provinces have issued forest fire alerts on fears of a repeat of last year's catastrophic blazes, which cost the country 16billion dollars.
Forest fires are an annual hazard in Indonesia and the resulting haze often impacts neighbouring Singapore, Malaysia and Thailand, driving air pollution to hazardous levels.
- DPA