No one was injured in the incident, which happened at 5.35 am, and none of the spilled oil has drifted to any of the islands or to mainland Singapore.

But the Maritime and Port Authority of Singapore (MPA) said an aerial check from 10.30 am to 1 pm showed two oil slicks in Indonesian waters, north of Bintan, measuring 2.5 km by 0.3 m and 2.5 km by 0.5 m.

Two smaller patches of oil were also seen off the coast of Bintan, and the MPA has informed the Malaysian and Indonesian authorities about them.

These spills are being cleaned up, the MPA said.

It added that initial estimates show that 350 tonnes of Sumatra Light crude oil had leaked from the 50,063 gross ton Singapore-registered tanker called The Agate.

An MPA spokesman said yesterday evening that the tanker had damage in its left port slop tank, but added that there was no further leakage.

The remaining oil from the damaged tank has been transferred to other tanks, and The Agate is now anchored close to where the collision took place.

The cargo ship it collided with, a 4,746 gross ton Panama-registered vessel called Tian Yu, had minor dents in its bow.

Four companies which clean oil spills have been mobilised and they have deployed six anti-pollution crafts to contain and recover the spilled oil.

Two sets of oil booms have also been laid to contain the oil slicks and stop it from spreading.

The MPA is monitoring the situation by deploying six anti-pollution crafts at the eastern fringes of Singapore's port limits.

It added that all port operations continue to function normally and shipping traffic within Singapore waters and the Singapore Strait remain unaffected.

Navigational broadcasts have also been issued to inform ships in the vicinity of the incident, advising them to keep clear.

The MPA is investigating the incident, the third one this year in which the collision of two ships led to an oil spill.

In June, a Thailand-registered freighter collided with a Singapore-registered bunker tanker, about 4.5 km south-east of Sentosa, spilling about 450 tonnes of marine fuel oil.

Less than a month later, in July, an India-registered oil tanker collided with a Panama-registered bulk carrier about 6 km south of the Tanah Merah Ferry Terminal, spilling 19 tonnes of light crude oil.