The 1-hour PM2.5 reading in the west reached 288 at 3pm, the highest since 2015.

Last Friday, the Haze Task Force said the masks would be distributed to more vulnerable individuals when the 24-hour PSI exceeded 200 and entered the very unhealthy range.

Masks are being made available progressively at designated collection points, including community clubs and vending machines.

Minister for Sustainability and the Environment Grace Fu noted that it might take "some time" for the machines to be fully rolled out across the island. "We urge the patience on the part of Singaporeans," she said.

The law criminalises conduct that causes or contributes to haze pollution in Singapore.

Speaking to the media on the sidelines of a mask distribution exercise at Yuhua Community Club, Ms Fu added, "We have to look at the data that we are collecting now, and the options are there for us to pursue."

These machines use living human brain cells grown on silicon chips and need nutrients and oxygen to survive. If they aren't fed, they die. Here's why researchers are going through all that trouble for these biocomputers.

The thumb-sized device, concealed in toilet paper, was discovered plugged into a USB port behind a television at OpenAI's San Francisco office on Sep 30.

Investigators later found a similar customised device in the man's personal bag.

Stuart Smith reports for CNA from London.