CHINA'S first aircraft carrier has left its shipyard in the northeast to start its first sea trial, the state news agency Xinhua said.

The revamped old Soviet ship's sea trial was in line with the schedule of the carrier's refitting project and would not take long, the news agency said, quoting military sources.

After returning from the trial, the carrier will continue its refit and test work, the report said.

Beijing last month sought to downplay the capability of its first aircraft carrier, saying the vessel would be used for training and "research", amid concerns over the country's military build-up.

The project has added to regional worries over the country's fast military expansion and growing assertiveness on territorial issues.

It also comes amid heightened tensions over a number of maritime territorial disputes involving China, notably in the South China Sea, which is believed to be rich in oil and gas and is claimed by several countries.

The issue has heated up recently with run-ins between China and fellow claimants Vietnam and the Philippines, sparking concern among its neighbouring countries and the US.