Four oil slicks, covering 101 square kilometers (38.9 sq miles), have been detected so far, four days after the oil tanker Sanchi exploded and sank in the East China Sea.
Data released by China's State Oceanic Administration on Wednesday night showed the existence of four scattered oil slicks, ranging between 5.5 and 48 square kilometers.
Excessive hydrocarbon levels have been detected in five water samples out of 19 collected by the agency near where the vessel went down, according to agency's most recent statement.
The Iranian oil tanker Sanchi, registered in Panama, exploded and sank on Sunday, eight days after colliding with the Hong Kong-registered bulk freighter CF Crystal, about 300 kilometers east of the estuary of the Yangtze River near Shanghai, on Jan. 6.
It sank about 280 km southeast of the point of collision after drifting for eight days, and currently it is at a depth of 115 meters (377.3 feet).
Several oil slicks appeared after the vessel sank. The Chinese Government has not yet said if they come from the ship's cargo, refined petroleum condensate, which is easier to clean, or if it is bunker fuel, which is more difficult to eliminate.
The tanker was carrying 136,000 tons of refined petroleum condensate and a good part of that cargo burned during the fire that consumed the ship for a week.
A total of 19 boats from different Chinese institutions are in the area for the control and cleanup work, while Japan and South Korea have also provided maritime resources.
The search for the 29 missing sailors was suspended after the explosion. The bodies of three of the 32 crew members have been retrieved.