The 30-vessel fleet set out from the southern Chinese province of Hainan yesterday, the Xinhua news agency said.
Chinese fishing boats regularly travel to the Spratlys, a potentially oil-rich archipelago which China claims as part of its territory on historical grounds.
But the fleet deployed yesterday is one of the largest ever launched from the province, according to the report.
China says it has sovereign rights to all the South China Sea, believed to sit atop vast oil and gas deposits, including areas close to the coastlines of other countries and hundreds of kilometres from its own landmass.
But Taiwan, Vietnam, Brunei, Malaysia, and the Philippines also claim parts of the South China Sea.
The Spratlys are one of the biggest island chains in the area.
The rival claims have long made the South China Sea one of Asia’s potential military flashpoints, and tensions have escalated over the past year.
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 Philippines said the latest example of this was at annual Southeast Asian talks in Cambodia that ended today in failure because of the South China Sea issue.
The Philippines had wanted its fellow Association of Southeast Asian Nations to refer in a communique to a recent standoff with China over a shoal in the South China Sea.
But Cambodia, the summit’s host and China’s ally, blocked the move.