Beijing: Rescue crews have scrambled to bring a blaze on an Iranian oil tanker off China's coast under control as fire raged for a second day after a collision with a grain ship, while the US Navy joined the search for 32 missing crew.

Concerns were growing that the tanker, which hit a freight ship on Saturday night in the East China Sea, may explode and sink as the inferno grew, the official China Central Television (CCTV) said on Monday, citing experts on the rescue team.

The extent of the environmental harm and size of the oil spill from the ship were not known, but the disaster has the potential to be the worst since 1991 when 260,000 tonnes of oil leaked off the Angolan coast.

The US Navy sent a military aircraft to assist with the search, which spanned an area of about 3,600 square nautical miles, but said in a statement it did not locate any of the tanker's missing crew members.