FUZHOU, April 7 (Xinhua) -- Four bodies have been retrieved a week after a ship capsized in the Taiwan Strait on March 30, leaving 13 people missing, the maritime bureau of southeast China's Fujian Province said on Tuesday.

The cargo ship "Zhenhe 168" sank on sea off Taiwan Xiquan Island at around 4: 40 a.m. on March 30. Rescuers from the Chinese mainland found three bodies at the ship's cabin between Saturday and Monday, while another one was retrieved by authorities from Taiwan on Sunday.

The ship's owner modified the ship's cabin and other parts and didn't register or undergo inspection, while most of the crew on board didn't hold competency certificates, initial investigations show.

The cause is still under investigation.