A strong burning smell was reported over several parts of eastern Singapore yesterday, including Tampines, Bedok and Pasir Ris.
In response to queries from The Straits Times, the National Environment Agency (NEA) said it had received reports of a smoky smell in the eastern part of the island.
Its investigations so far have not detected any local sources of burning or incidents at factories that could have contributed to the smell, said its spokesman, adding that no sources of transboundary haze were detected in the region.
"We are closely monitoring the air quality and will provide updates of any further findings or significant change to the air quality situation," he said.
Tampines resident Jon Lee, 45, likened the smell to that during the haze or of offerings being burned during the Chinese seventh month.
"I was taking my son to school... at around 6am, and there was a strong burning smell. At 7am, when I dropped my son off in the East Coast area, it was still there," said Mr Lee, who works in sales. He added that there was no burning smell when he reached his workplace in the west, and that his colleague, who lives in Bedok, also described a similar burning smell.
A reader, who wished to be known only as Ms Tan, 24, said she noticed the smell at the void deck of her Tampines home after 7am.
Netizens posting on online forum Reddit said Simei, Pasir Ris, Bedok, Tampines and Marine Parade were among the areas affected, with some noticing the smell from as early as 3am.
"The smell was pretty strong, and when I got to the bus stop I could see that it was a bit hazy. Things looked blurry from a distance," said the trainee teacher.
Another reader who did not wish to be named also noted a strong burning smell which, she said, was similar to the haze.
"I smelt it once I woke up around 7.30am and stepped out of my room. I went to the balcony to see if someone was burning something, but I didn't really see anything," said the 23-year-old, who works in public relations.
Netizens posting on online forum Reddit said Simei, Pasir Ris, Bedok, Tampines and Marine Parade were among the areas affected, with some noticing the smell from as early as 3am. Facebook user Han Han, in a post at about 7.25am, said it had a "burnt leaves" smell.
When The Straits Times reached Tampines at about 8.30am, a strong burning smell was in the air. Some pedestrians were spotted donning face masks at Tampines Central Park. It was hazy in the area, with buildings in the distance appearing unclear and obscured.
At least one ST reader said the smell reached the Bukit Timah area in the early morning. The reader, who wanted to be known only as Mr Jeevan, 65, a businessman, said he could smell it while jogging from his home in Jalan Jurong Kechil to the Beauty World MRT Station.
"I was starting my daily early morning jog at about 4.45am, and the smell was very strong. I thought at first that someone was burning offerings," he said.
He added that the smell seemed to have subsided by about 5.15am.
In its statement, NEA said the one-hour PM2.5 readings in the east from 4am to 5am ranged from 70 to 73 micrograms per cu m (mcg/m3), in the "elevated" range. PM2.5 is the dominant pollutant during haze episodes.
This dropped to the normal range from 6am to 7am, with readings ranging from 19 to 26 mcg/m3.
But it rose again from 8am to 11am to "elevated", ranging from 46 to 62 mcg/m3. The one-hour PM2.5 readings in other regions of Singapore were in the normal range over the same periods of time.
As at 5pm, the 24-hour PSI was 65, in the moderate range.
And as at 7pm, the Singapore Civil Defence Force said it had not received any reports of incidents that may have caused the smell.
Some ST readers in Pasir Ris and Tampines said the smell was back at around 10pm.