China has sent one of its largest recorded fishing fleets to disputed islands in the South China Sea, state-run media said on Tuesday, amid tensions over Beijing's assertion of its claims in the region.

A flotilla including 30 fishing vessels set sail on Monday for the Spratly Islands, an archipelago disputed between China and other countries including Vietnam and the Philippines, the China Daily reported.

The fleet left China's southern province of Hainan for a 40-day trip to the region, the report said, and includes two large transport and supply ships.

Chinese fishing boats regularly travel to the Spratlys, parts of which are also claimed by Taiwan and Brunei, but the fleet dispatched Monday was as large as one described as the biggest ever launched from the province when it set off last year.

China will make "every effort to guarantee the fleet's safety," the report quoted an official from the department of ocean and fisheries as saying.

China and neighbouring countries have long used fishing fleets and maritime patrols to assert their territorial claims, and have upgraded their naval forces in recent years as tensions over claims in the South China Sea have risen.

The Philippines and Vietnam have complained that China is becoming increasingly aggressive in its actions in the area -- such as harassing fishermen -- and also through bullying diplomatic tactics.

The waters around the Spratlys are rich in fishing resources and it is believed they could hold large oil and gas reserves.