SHANGHAI – Chinese authorities said they have been able to contain a spill from oil tanker Sanchi in the East China Sea within an area of 30 square kilometers (11.6 square miles) from 328 sq km, according to local media reports.

A month ago the tanker – which was carrying 136,000 tons of refined petroleum oil and also some 1,900 tons of fuel oil – had collided with freighter CF Crystal and exploded into flames, leading to a large oil spill.

Five Chinese, one Japanese and one South Korean ships had cleared a total of 225.8 square nautical miles until Tuesday, a Transport Ministry official, Zhi Guanglu, said at a press conference in Beijing Thursday.

“We are also making plans to clean residual oil underwater with the help of underwater robots to root out the hidden risks from the oil spill,” said Zhi.

He added China’s marine, environmental and agricultural authorities have been monitoring the situation closely, and up to 800,000 sq. kms of sea surface has been examined with the help of 500 samples of water from 40 locations.

Sanchi had sunk on Jan. 14, some 530 kilometers to the southeast of Shanghai, killing all 32 sailors on board.

Rescue teams have been able to recover the bodies of only three victims so far.

Experts have warned this could be one of the worst environmental disasters in recent times, although China is yet to release any official information regarding this.