Stronger action is needed to prevent the haze from returning, said Minister for the Environment and Water Resources Masagos Zulkifli yesterday.

This comes even as rain brought relief and air quality here is expected to enter the good range for the first time since it hit unhealthy levels two weeks ago.

In a Facebook post, the minister called for stronger action to prevent what he said was the "perennial scourge for South-east Asia" from recurring.

Noting that the Indonesian government is reportedly "investigating several companies, including Singapore-based ones", Mr Masagos said the National Environment Agency (NEA) has already written to its Indonesian counterpart to request more information, so that the Republic can investigate on its end.

"We will not hesitate to enforce the Transboundary Haze Pollution Act if Indonesia is able to provide Singapore with evidence of wrongdoing by any company that has contributed to haze in Singapore," he wrote.

"Singapore will not tolerate the actions of errant companies that jeopardise the health and lives of people here and in other countries, and which set back our efforts to fight climate change."

He added that Singapore conveyed its concerns over the rise in hot spots, as well as offered its assistance, to the Indonesian government last week.

In an update yesterday evening, NEA said that for the next 24 hours, the 24-hour Pollutant Standards Index (PSI) is forecast to be in the good to moderate range.

This means that air quality could enter the good range in some parts of the Republic for the first time since it hit unhealthy levels two weeks ago.

Air quality took a sharp turn for the worse here on Sept 14 when the 24-hour PSI reading crossed the unhealthy level for the first time since 2016.

It has remained in the moderate to unhealthy range since then.

The one-hour PM2.5 concentration reading, which the agency has said is a better indicator of current air quality, is expected to be in the normal band, although it may occasionally enter the elevated band.

NEA said that the likelihood of the haze affecting Singapore is low, noting that thundery showers are forecast over Singapore and in parts of Sumatra for the next few days.

Still, there could be slight haze here in the next few days if winds shift to blow smoke from Sumatra.

At 10pm yesterday, the 24-hour PSI reading was 65-74, in the moderate range. The PM2.5 reading was 21-40, in the normal band.