Though slight now, the haze could worsen in the coming months, and peak in September, deep into the dry season.

Yesterday, 32 hotspots were detected in Sumatra, and 50 in Borneo. Meteorologists are watching as an early-stage El Nino develops over the Pacific Ocean.

'It is cause for concern because it means the haze situation could worsen,' said Dr Yaacob. 'We are already seeing some signs of it.'

In fact, all it would take now for haze to blow by is for the wind to change, said experts. It has already blanketed parts of neighbouring Malaysia.

The pollution standards index (PSI) peaked at an unhealthy 136 in areas such has Port Klang, Shah Alam and Cheras last week, as visibility and air quality deteriorated rapidly.

In Singapore the PSI is in the good range for now.

But similar hot and dry weather in 1997 and 2006 fuelled fires in Indonesia, and south-westerly winds sent the smoke onwards.

The haze lasted three months in 1997, with the PSI reaching an all time high of 226 in September. People stayed indoors, healthcare costs soared and tourism was disrupted.

According to a World Wide Fund for Nature (WWF) report published in 1998, Singapore, Indonesia and Malaysia suffered more than S$2.1 billion in the toll to their economies.

Read the full report in Saturday's edition of The Straits Times.