Residents of Singapore rejoiced Saturday as thick smog from forest fires in Indonesia gave way to a spell of blue skies and smoke-free air, but the government warned it was a temporary respite.

The pollutant standards index (PSI), which stood at hazardous levels above 300 early Saturday, progressively dropped to a moderate 73 by late afternoon in the densely populated city-state of 5.3 million people, more than a third of them foreigners.

Shoppers eagerly returned to posh shopping district Orchard Road -- many still with their protective face masks on -- as the skies started to clear during lunchtime and social media postings were full of cheerful messages after days of gloom.

Residents of private condominiums began using their swimming pools and tennis courts again.

However, broadcaster Channel News Asia's website quoted the environment agency as saying that the improvement "was due to a temporary area free of dense haze upwind of Singapore" and "transient changes in the local wind conditions" before the haze returns on Sunday.

Shawn Lim, 22, said he was taking advantage of the situation to go outdoors to distribute protective masks to those who have not been able to get their hands on one due to a run on the products.

"I am going around City Hall this evening to give out masks to people who don't have them," said the media executive.

"It is great that the weather is clear, I am enjoying it while I can before the haze comes back."

Law student Akesh Abhilash, 25, said he was planning to play football with friends if the PSI remained within double digits in the evening.

Some however erred on the side of caution, fearing that the air was still unhealthy.

Lecturer Gangasudhan, 36, said he was going to spend the evening indoors as "looks can be deceiving".

While the PSI had gone down, Gangasudhan, who goes by one name, cited another reading -- the concentration of fine particles measuring 2.5 micrometres or less -- which remains at a high level across the island nation.

"I am going to wait for the PM2.5 level to drop to safer levels before resuming normal activities," he said.

Smog from forest fires in plantations and fires on Sumatra island are blown to Singapore and Malaysia by monsoon winds during the June-September dry season.

The index has been fluctuating since reaching unhealthy levels on Monday.

On Friday, much of the population retreated indoors and when the index hit a record 401, which could have been life-threatening to the ill and elderly if it had lasted 24 hours.