SINGAPORE - Photos circulating online of a double bed squeezed at the bottom of a large drain in Bukit Panjang have prompted the authorities to investigate possible signs of habitation, with water agency PUB referring the case to the police.

The photos showed a bed, on a metal frame, placed snugly in a narrow channel. Some plastic bags, rubbish and what appeared to be shoes were seen as well.

Responding to queries from The Straits Times on Monday (Oct 30), PUB said it "is aware of the possible human dwellings in the drain along Kranji Expressway".

"The items have since been removed and we have referred the case to the police, who are looking into the matter," PUB added.

The drain is reportedly located near West Spring Secondary School and Senja Road.

Shin Min Daily News said the area is near a construction site.

A construction worker who gave his name only as Mr Rahim told Shin Min that he had seen three men living in the drain.

"I saw three men living there before, they stayed there for two to three months, and carried a small backpack with them," he said. "We've seen them sleeping on the bed in the morning, but after that they were nowhere to be seen."

The foreman at the construction site told Shin Min that the drain was cleared of items and garbage last week.

PUB stressed that "members of the public are not allowed to enter drains at all times for their personal safety".

"Heavy rainfall in upstream locations will cause sudden and rapid water flow into the drain," said the spokesman. "This will pose a serious danger to those in the drain."

Those who are found entering waterways without prior approval can be fined up to $3,000.