QIONGHAI, Hainan, May 7 -- Contact with 11 fishermen has been lost after they were intercepted by armed men in the South China Sea on Tuesday morning, local authorities said Wednesday.

They were on board fishing boat Qiongqionghai 09063, which was intercepted by an unidentified armed vessel at about 10 a.m. in waters off the Half Moon Shoal of Nansha Islands, according to the Tanmen fishing association in Qionghai City, Hainan Province.

Several armed men forced themselves onto the boat and fired four or five shots in the air. They then took control of the boat, according to the association.

Another nearby fishing boat, Qiongqionghai 03168, rushed away after seeing the armed boat. It encountered another armed boat later but successfully escaped, according to the association.

The Qionghai municipal government has mobilized two nearby fishing boats to search for the missing fishermen but failed to find the boat as of Wednesday morning.

The Half Moon Shoal is a major fishing base for Chinese fishermen.