[UPDATED 20 June, 10pm: 3-hour PSI reading back at 231, within the "very unhealthy" range, at 10pm Thursday, after hitting a new all-time high of 371 at 1pm]
The Pollutant Standards Index (PSI) hit a new record high of 371 at 1pm on Thursday, again climbing into the "hazardous" range of above 300, according to data from the National Environment Agency (NEA).
At 9pm Wednesday, the PSI had soared to 290, higher than the previous peak of 226 in 1997, and entering the "very unhealthy" range of 201-300. It was a leap of 100 points from the PSI reading just an hour earlier, making some wonder if the updated reading was a typo on the NEA website.
"I thought it was actually worse in the day, though -- seems pretty impossible that there would be a hundred-point jump within an hour, coupled with the fact that it isn't that windy in the first place," said systems analyst Frederick Tang, 36.
"I thought it was a mistake at first," added communications undergraduate Gina Foo, 21, who said she had been feeling "very uncomfortable" while travelling outside during the day. "But I will definitely be wary about my plans for tomorrow, given how unpredictable the situation is."
NEA's guidance for when haze reaches the hazardous level is for children, elderly and persons with existing diseases to stay indoors and avoid outdoor activity. "The general populationshould avoid unnecessary outdoor activity," it said.
Meanwhile, masks and air purifiers flew off the shelves at pharmacies and medical stores on Wednesday while others venturing outside experienced a range of ailments.
"You can actually feel the haze now -- the smoke and dust particles in your eyes," said 24-year-old Ronald Loh, who was travelling around the Tampines area. "It's especially bad for people wearing contact lenses or with eye problems."
"I can smell the haze in all my clothes and towels, even though they were hung inside," added Tang.
"It's getting very hot, the fan and aircon not enough and I'm having breathing problems already," said homemaker Yasmin Abdul Razak, 47. "But nothing we can do, just wear a mask and life goes on."
27-year-old Chloe Liaw, a medical sales executive, called for action from the authorities: "Something really needs to be done at the government level, to fix this problem."
"There is nothing much we can do about it, other than dying slowly in the poor air quality," she lamented. "At least provide free N95 masks for everyone?"
The PSI has been climbing steadily since Monday from 55 at 9am to 80 at 12pm and crossed into the "unhealthy" range of 105 at 3pm, according to the National Environment Agency (NEA).
Any reading between 101 and 200 is considered “unhealthy”.
The smoky-smelling haze from Indonesia shrouded skylines and was visible on street level at various places. Marina Bay Sands was cloaked in smoke as the burnt smell pervaded the central business district.
The haze, brought about by prevailing winds from the fires in Indonesia’s Sumatra island, has affected Singapore since 13 June 2013 and is expected to continue over the next few days.
Environment and National Resources Minister, Dr Vivian Balakrishnan urged Indonesians "to enforce their own laws" in a Facebook post on Monday night.
"We are deeply concerned that the 113 hotspots in Sumatra have caused our 3 hour PSI to rise to 152. NEA has been in touch with the Indonesian authorities to register our concern, and renew our offer of assistance," he wrote.
"For too long, commercial interests in Indonesia have been allowed to over ride environmental concerns," he added, saying he would personally speak to his counterpart in Indonesia to "personally to convey the seriousness of the situation."
The last time Singapore saw such choking smog was in 1997, when the PSI index peaked at 226.
NEA advises on its website that people with existing heart or respiratory ailments should reduce physical exertion and outdoor activity. So far, the haze has not affected business or air transport.
Over the weekend, the haze situation also hit “unhealthy” levels in neighbouring Malaysia. The Malaysian pollutant index showed readings of 102 and 121 in parts of Pahang, Terengganu and Malacca on Monday.
Singapore experiences hazy weather conditions on a yearly basis when winds from Indonesian forest fires blows over the region during periods of persistent dry weather conditions.
The last time the PSI went over 100 in Singapore was on October 21, 2010, when it hit 106, according to local media.