BEIJING (REUTERS) - Contact has been lost with 11 fishermen in the South China Sea after they were intercepted by"armed men" and their ship seized in waters not far from the Philippines, China's state news agency Xinhua reported on Wednesday.

They were on board the fishing boat Qiongqionghai 09063, which was intercepted by an unidentified armed vessel at about 10 am (0200 GMT) in waters off Half Moon Shoal in the Spratly Islands, Xinhua said, citing a fishing association in Qionghai on China's southern island province of Hainan.

The shoal is some 100 km (60 miles) from the Philippines' Palawan island.

"Several armed men forced themselves onto the boat and fired four or five shots in the air. They then took control of the boat," Xinhua said.

A second fishing boat escaped, but then encountered another armed boat, though it was able to get away, the report added.

The Qionghai government has sent other trawlers operating close by to help look for the fishermen, but has yet to find them, Xinhua said.

Reuters was not immediately able to reach officials in Hainan for comment. It was also unclear from the report if the fishermen were Chinese nationals.

China claims almost the entire oil- and gas-rich South China Sea, rejecting rival claims to parts or all of it from Vietnam, the Philippines, Taiwan, Malaysia and Brunei. There are frequent tensions in the South China Sea between China and the other claimant nations, particularly Vietnam and the Philippines, both of which say Beijing has harassed their ships in the waters there.

On Tuesday, China warned Vietnam not to disturb activities of Chinese companies operating near disputed islands in the South China Sea, after Hanoi condemned as illegal the movement of a giant Chinese oil rig into what it says is its territorial waters.