The oil spill from sunken Iranian tanker Sanchi off the East China Sea has spread further, and Chinese authorities have deployed more vessels for the clean up operation.

The tanker, which was carrying 136,000 tonnes of light crude oil, sank in the East China Sea on Sunday, a week after colliding with Chinese bulker CF Crystal.

According to the State Oceanic Administration of China, it has spotted four separate oil slicks with a total area of nearly 101 sq km, increasing significantly from 69 sq km of oil slicks found on Tuesday. The administration is monitoring the marine pollution situation by collecting water samples from over 30 spots near the incident site.

The Ministry of Transport has deployed another two vessels for oil spill response work, adding to 13 vessels already in the operation.

Both the crude oil and the bunker fuel in the vessel could cause devastating damage to marine life, a number of NGOs have warned.

A team of marine engineers is now working on plans to stop the leak from the sunken ship and will deploy subsea robots to assess the damage of the shipwreck, which lies at a depth of around 115 m.