Singapore has registered its concern with the Indonesian government over the rising number of fire hot spots in Sumatra, most of which are in Riau, the National Environment Agency said.

The agency's chief executive Ronnie Tay contacted his Indonesian counterparts on Monday to express Singapore's concerns over a possible repeat of last month's smoke haze, when air quality here was the worst ever recorded.

He sought an urgent update of Indonesia's efforts to tackle the fires there and urged Indonesia to take immediate action, reiterating Singapore's offer to provide support in early detection of hot spots and fire suppression, and renewed Singapore's standing offer of an aircraft to help with cloud seeding operations.

Indonesian Deputy Minister for Environment and Social Vulnerability, Coordinating Ministry for People's Welfare, Mr Willem Rampangilei, said there was new sporadic burning.

Mr Rampangilei assured Mr Tay that the Indonesian government is monitoring the situation and taking action, such as by cloud seeding and water bombing, and that the government would urgently consider deploying additional police and troops to Riau, the NEA said.

On Monday, 252 hot spots were recorded in Sumatra, with 167 of those in the Riau province. At the peak of last month's haze episode, more than 400 hot spots were detected at a go.

Winds blowing towards Singapore have come generally from the south, so the skies remain clear. But if the wind direction changes to come from the west and south-west, the haze may return.