An Iranian oil tanker ablaze off the Chinese coast is at risk of exploding or sinking, as officials reported there were no signs of survivors 36 hours after the vessel erupted in flames.

A huge fire was still raging around the stricken ship, which had been carrying 136,000 tonnes of light oil, or about 1m barrels, with fierce heat and thick black smoke billowing from the vessel and the surrounding sea, reports theguardian.com.

Rescuers from three countries attempting to reach the crew of 30 Iranians and two Bangladeshis were being beaten back by toxic clouds and intense fires, China’s transportation ministry said. The Korean coastguard sent a ship to the scene but said bad weather was also hampering the rescue efforts. A US navy aircraft took part in the search on Sunday, scouring a large area before returning to Kadena airbase in Okinawa, Japan.

The Panamanian-flagged 274m (900ft) tanker Sanchi is ‘in danger of exploding or sinking’, the Chinese ministry said.

The accident happened on Saturday evening 160 nautical miles (300km) east of Shanghai.

The fire poses a serious environmental risk for the region. The ship was carrying condensate, an ultralight version of crude oil that converts from a gas to a liquid during extraction.

Condensate is in liquid form only under specific conditions. Although the damage has been difficult to fully assess, Korean coastguard officials say much of the condensate may have evaporated or burned off in the aftermath of the crash.

But any oil that did leak into the ocean will be harder to clean up, since condensate mixes more easily with water compared with traditional crude oil.

The tanker was heading to South Korea when it collided with a Hong Kong-flagged cargo ship, the CF Crystal, carrying 64,000 tonnes of grain. Ten government vessels and ‘many fishing ships’ were helping with the continuing rescue and clean-up effort, the Chinese ministry said.

Iran’s oil ministry said the tanker was operated by the National Iranian Tanker Company (NITC) and was delivering its cargo to South Korea’s Hanwha Total. The ship and its cargo were insured, a statement said. The oil was worth about £45m at current prices.