Two oil tankers caught fire off its coast and two crew members were airlifted to a hospital, according to the Maritime and Port Authority of Singapore's release.
The blaze broke out on board Singapore-flagged tanker Hafnia Nile and another vessel about 55 kilometres (34 miles) northeast of Pedra Branca.
"MPA has requested passing vessels to assist in the search and rescue of the crew," the authority said in a statement, adding that the RSS Supreme and a military helicopter were providing assistance.