SINGAPORE - The haze here on Monday was exacerbated by unfavourable winds, Environment and Water Resources Minister Vivian Balakrishnan said on Monday.
But rain over the next few days should improve the situation, he added.
The National Environment Agency said the air here should remain healthy on Tuesday as the 24-hour Pollutant Standards Index (PSI) is expected to be in the "good" range.
"Singapore may experience slightly hazy conditions in the morning, but all people can continue with normal activities," the agency said in an advisory.
The three-hour PSI reading climbed to 48 at 3pm on Monday, just shy of the "moderate" range of 51-100, before falling again in the evening.
People around Singapore complained of hazy conditions and a burning smell in the air in the afternoon.
Dr Balakrishnan said in a Facebook post on Monday night that the "visible haze" was partly due to south-westerly winds blowing from hot spots or fires in Riau province, Indonesia.
The number of hot spots in Sumatra had risen over the weekend from about 25 to 33, according to satellite maps, but some could have been obscured by cloud cover.