China's first aircraft carrier has left the shipyard for a long-awaited sea trial.

The refitted old Soviet vessel left the northeastern port of Dalian early Wednesday. Officials said the trial was on schedule and that afterwards the ship will dock for further work.

Concerns were raised about China's military build-up when it purchased the stripped-down hull of the vessel from Ukraine in 1998. China's defense ministry said last month that the carrier will be used for training and research.

The carrier was originally built by the Soviet Union, but was not completed before the communist state collapsed in 1991. The vessel was subsequently transferred to Ukraine, which sold it to China after stripping most of its fittings.