A worker was hospitalised on Saturday after he fainted in a tank aboard a crude oil tanker that was docked in Singapore for repairs.

The incident happened on the M/V Pavinospirit, at the Sembcorp Marine Admiralty Yard.

Sembcorp Marine's Health, Safety and Environment team received a call for assistance from the vessel at 4pm on Saturday, a spokesman said.

The worker was employed by a contractor engaged by the shipowner to conduct "thickness measurement" of tanks on board the Pavinospirit.

He fainted at the bottom of the tank that he and three other men had been working in.

A photo of the victim sent to The Straits Times showed his head and torso to be covered entirely in what looked like thick, black oil.

The Sembcorp Marine spokesman said the tank had a thin layer of oily residue at the time.

"The...worker was consequently evacuated to the ship deck and taken to Khoo Teck Puat Hospital immediately," said the spokesman.

The Straits Times understands the victim was in the Intensive Care Unit.

The other three workers are reported to be well.

The shipyard is assisting the authorities with investigations, said the Ministry of Manpower.

The Pavinospirit is sailing under the flag of Russia, according to vesselfinder.com.