Indonesia on Tuesday released waterbombs to put out forest fires in Riauprovince, in a bid to fight the haze that has caused one of Southeast Asia's worst air pollution crises.

Firefighters were also on site in Bengkalis, one of the areas in the province with the highest number of fires.

Indonesia's environment minister said eight domestic firms were suspected of being responsible for the blazes on Sumatra island that blanketed neighbouring Singapore in record levels of hazardous smog.

Authorities said they started cloud-seeding operations last week and it induced a 20-minute rain shower in the capital of Pekanbaru on Tuesday afternoon, the first rainfall in a month.