HANGZHOU -- Eight fishermen are missing and six were rescued after their vessel sank in the East China Sea, maritime safety officials said on Thursday.

The vessel dropped anchor 80 nautical miles from the coast early on Wednesday and the maritime authorities of Zhoushan, east China's Zhejiang Province, lost contact with it at 7:00 a.m., according to the Zhejiang provincial maritime safety administration.

Thirteen lifeboats are searching for the missing fishermen, while the six rescued were on their way to land on Thursday morning.

The cause of the sinking of the Zhejiang-registered vessel is still unknown. An investigation is underway.