Two large oil tankers were on fire on Friday after colliding near Singapore.
A pair of crew members had to be airlifted to hospital and others rescued from life rafts, authorities and one of the tanker owners said.
The Singapore-flagged tanker Hafnia Nile and the Sao Tome and Principe-flagged tanker Ceres I were about 55km northeast of the Singaporean island of Pedra Branca on the eastern approach to the Singapore Straits when they collided.
The Maritime and Port Authority of Singapore (MPA) said all 22 crew of the Hafnia Nile and the 40 on the Ceres I were all accounted for.
Smoke could be seen from one of the freighters
Republic of Singapore Navy via Reuters
Navigational traffic had not been affected, although the status of the vessels or any pollution was unknown at present, a spokesperson at the UN's International Maritime Organization (IMO) said.
"No aerial surveillance has been conducted so far," the spokesperson said.
"Salvage and fire-fighting assets have been arranged by both vessel owners to support the fire-fighting efforts and subsequent towage of the vessels to safety."
The IMO spokesperson said a salvage team had been appointed and was en-route to the area.
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The area Ceres I is anchored in is known to be used by so-called dark fleet ships for the transfer of Iranian oil in contravention of US sanctions, said Michelle Wiese Bockmann, principal analyst at Lloyd's List Intelligence.
"The Ceres I has repeatedly been involved in transferring or shipping Iranian oil in breach of US sanctions," she said.
Shipping sources have said the tanker was also involved in transporting Venezuelan oil, which is also under US sanctions, to China in recent years.
Up to 850 oil tankers are estimated to operate the shadow fleet transporting oil from countries such as Iran and Venezuela as well as Russia, which has multiple restrictions on its oil exports.
A spokesperson with the International Maritime Organisation said: "Salvage and fire-fighting assets have been arranged by both vessel owners to support the fire-fighting efforts and subsequent towage of the vessels to safety. Navigational traffic is not affected."
