A strong odour that smelt like burning chemicals or petrol, along with smoke that stung the eyes, fanned anxiety among many yesterday as it spread from north-eastern parts to the western areas of Singapore.
Many remain puzzled at the lack of details over the source of the smell and smoke, despite assurances from the National Environment Agency (NEA) and the Singapore Civil Defence Force (SCDF) yesterday that there were no toxic industrial substances in the air and that air quality during the period had been well within safety limits.
From as early as 4pm, people living in northern areas, including Seletar, Yishun and Sengkang, started reporting about the acrid smell and the smoke, which spread to central areas like Bishan and Ang Mo Kio around 6pm and to western areas like Clementi and Bukit Timah around 8pm.
More than 10 readers wrote to The Straits Times about a "burning", "chemical" or "petrol" smell.
One of them was Ms Lelavathi Annamali, an Ang Mo Kio Avenue 8 resident who said she started smelling "a very strong kerosene smell" at around 6pm, and that her home became very smoky, which stung her eyes and affected her throat.
"The smell is very bad inside the house and is affecting the clothes, too," said the 68-year-old retiree.
Bishan resident Jacky Kung, an 18-year-old student, said he started smelling a petrol-like smell from 4pm. "I could feel my throat drying out and it felt a bit uncomfortable and choking," he said, adding that he had to close all the windows.
Ms Tina Lim, 49, who works in a bank, said there was a "very strong burnt smell" when she reached her Sengkang home at about 5.30pm. "It didn't smell like haze," she said. "It was like something is burning."
Mr Osman Ahmad, a 59-year-old security guard at Seletar Country Club, told ST he noticed the smell of burning chemicals when he left his home in Pasir Panjang around 2pm.
When he stopped to change buses at Seletar, he noticed that the stench was stronger and that people at the bus stop were covering their mouths and noses with tissue paper and handkerchiefs.
"You could see a layer of smoke on the highway. It looked like a morning fog, which was beautiful but very smelly," he added.
The SCDF and NEA had deployed officers to investigate upon receiving calls.
The SCDF said at 9.55pm that its monitoring teams have not detected the presence of toxic industrial chemicals in the air.
In an update at 10.34pm, the NEA said it had received feed-back from the public about a gas smell in Sengkang and Punggol around 5pm.
"NEA officers were deployed to those areas immediately to investigate the smell feedback," it said, adding that air quality levels during the period were found to be well within safety limits.
The NEA also said that winds had converged over the northern half of Singapore from about 3pm, which may have led to smells accumulating in the northern area.
"Winds are expected to turn to blow from the south or south-east later tonight, which will help to disperse any smells in the area," said the NEA, adding that it would continue to monitor the situation closely.
The Straits Times understands that the fumes are believed to be from Johor Baru.