The haze in Singapore worsened considerably on Wednesday afternoon, with the Pollutant Standards Index climbing to 170 in the "unhealthy" range at 2pm. Air becomes very unhealthy when the index passes 200.
The current smog is the worst since 1997, when the index hit 226. 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.
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.
In an interview with BBC News on Wednesday morning, 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.
Dr Balakrishnan told BBC that Singapore companies in Indonesia would also be punished if they were found guilty. "I've spoken to my colleagues in Indonesia, and I told them if they have evidence to name the specific companies, I will take action against them," he said.