The three-hour Pollutant Standards Index (PSI) at 7pm on Saturday rose slightly to 77, up from 73 an hour earlier.

The 24 hour average PSI at 7pm also dipped to a 161-182 range from 165-185.

Air in the 51-100 reading is considered "moderate", while the 101 to 200 PSI range is considered "unhealthy". Anything above 300 is hazardous, while readings between 201 and 300 are very unhealthy.

The National Environment Agency (NEA) said they expect PSI readings to remain in the "very unhealthy" range of 201-300 for the next 24 hours. The public, especially the elderly, pregnant women and children, and those with respiratory or heart problems, are advised to refrain from prolonged outdoor activity and to wear an N95 mask while outside.

For the past few days, record-high PSI readings have sent N95 face masks flying off the shelves.

Besides masks, those looking for succor from the haze turned to their neighbourhood herbal shop. At the Toa Payoh Central branch of Hock Hua Tonic, there seemed to be an endless crowd around the shop's herbal drinks stand.

Store manager Don Goh, 44, said sales of prepared tonic drinks had shot up 50 per cent in the last week, with certain flavours like chrysanthemum tea moving 500 bottles in a day. The increase in dry herbs was even greater, he added, with a 100 per cent increase in sales.

"The only time sales is better is during Chinese New Year," he said.