Singapore's smog index hit the critical 400 level on Friday, making it potentially life-threatening to the ill and elderly people, according to a government monitoring site.
The record level was reached at 11:00 am (0300 GMT) after a rapid rise in the Pollutant Standards Index (PSI), which measures the haze crisis caused by Indonesian forest fires.
Indonesian and Singaporean officials have been holding emergency talks on how to extinguish the fires on farms and plantations on Sumatra island, which are also affecting Malaysia.
According to Singapore government guidelines, sustained PSI average levels above 400 on a 24-hour basis "may be life-threatening to ill and elderly persons".
General practitioner Philip Koh said he had seen a 20 percent spike in consultations in the past week, and estimated that about 80 percent of all his patients are suffering from haze-related ailments.
"My patients are telling me they are worried about how long this is going to last and how much higher this is going to go. It is already high at 400 now, how much higher will it go?" he told AFP.
Koh also said many were turning to his clinic to buy protective masks, as supplies are low at retailers.
"Our supplies are running low here too," he said.
If the 400 index average is sustained over a 24-hour period, the government advises all children, elderly people and persons with existing diseases to stay indoors, keep windows closed and avoid physical exertion as much as possible.