China, Iran, Panama and Hong Kong signed an agreement on Thursday to investigate the sinking of an oil tanker in the East China Sea, the Ministry of Transport said.

The agreement was based on global shipping regulations, safety investigations and standards from the International Maritime Organization.

Stakeholders will be invited to participate in and witness restoration of the ship's "black box", and contact will be enhanced with the International Maritime Organization to ensure an objective investigation, Zhi Guanglu, deputy director of the China Maritime Search and Rescue Center, part of the Ministry of Transport, said at an earlier news conference.

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

The Sanchi had 32 crew members－30 Iranians and two Bangladeshis. Three bodies have been found, according to the ministry. The cargo ship's 21 crew members were rescued.

Cleanup work has been ongoing. On Wednesday morning, a silver and white oil slick 1,800 meters long and 300 meters wide was discovered about 200 meters southeast of the sunken vessel. At noon on Wednesday, an oil slick measuring 1,000 meters long and 300 meters wide was seen about 2 km from the site, according to the State Oceanic Administration.

Since Sunday, the size of the oil slicks have shrunk, the administration said.