SINGAPORE'S air is now on the cusp of being "hazardous" as the Pollutant Standards Index soared to 290 at 9pm, the worst reading ever in the Republic.

Air becomes hazardous when the index passes 300. The worst smog reading before this was 226, in 1997.

Several organisations such as the Singapore Civil Defence Force, Singapore Armed Forces and Ministry of Home Affairs have all reduced physical and outdoor training in light of the health risks, while NTUC FairPrice has issued face masks to all of its pump attendants at its petrol stations.

Earlier on Wednesday, Environment Minister Vivian Balakrishnan acknowledged that Singaporeans are "very frustrated, angry and distressed about the situation".

Both Dr Balakrishnan and Foreign Minister K. Shanmugam spoke to their Indonesian counterparts on Tuesday to urge them to take tougher action against companies responsible for the illegal burning.

The National Environment Agency said on Tuesday night that haze is likely to last for the next few days, and is the result of fires in Sumatra, Indonesia.