The water quality in the East China Sea where an Iranian tanker sank over three weeks ago, causing an oil slick, meets the highest Chinese standards, the maritime authority said on Saturday.

The State Oceanic Administration said in a statement that a 2.4-kilometer-long silver-white oil slick was detected about 1 km southeast of the sunken vessel Sanchi at 8 am on Saturday.

Seawater samples were collected from 17 measuring points around the site from Friday afternoon to Saturday morning as a continuation of the monitoring work of the surrounding seawater quality, the administration said.

The test results showed the seawater conforms to all relevant water quality requirements of the first category, the highest standard in China, including the oil concentration levels of the surrounding seawater.

The seawater quality standard, which has been used by China's environmental and oceanic administrations since 1998, specifies the water quality requirements grouped into four categories of application functions for Chinese maritime areas.

The first category applies to fishing waters, nature reserves and rare and endangered marine conservation areas, while the second applies to aquaculture zones, popular bathing beaches and industrial water-use areas directly related to human consumption.

The third category applies to general industrial water-use areas and scenic seashore spots, and the fourth applies to marine port and marine development zones.

The Panama-registered oil tanker Sanchi, which was from Iran and had been carrying 111,300 metric tons of highly flammable condensate oil, collided with a Hong Kong cargo ship around 8 pm on Jan 6 some 160 nautical miles east of Shanghai.