BEIJING (AP) ― China’s first aircraft carrier swept through fog-shrouded waters Wednesday to open sea trials that underline the country’s big naval ambitions and fuel concerns about its growing military strength amid regional territorial disputes.

The ship is former Soviet craft that China acknowledged a month ago it was rebuilding for research and training, in a strong indication that it plans to start building aircraft carriers of its own.

China has been investing heavily in modernizing its military for at least the last decade, and having its own carrier will add prestige to that expansion, which has accompanied a rise in nationalism in the country.

The carrier left Dalian port in northeast Liaoning province early Wednesday, the official Xinhua News Agency reported.

Xinhua said the first sea trial was in line with the country’s schedule to rebuild the carrier. China has spend the better part of a decade refurbishing the former Soviet aircraft carrier Varyag after it was towed from Ukraine in 1998, the report said, citing unnamed military sources.

China’s carrier ambitions have sparked concern among neighbors amid heightened tensions over territorial disputes around Taiwan and in the South China Sea.

Over the past year, China has seen a flare-up in territorial spats with Japan, the Philippines and Vietnam and had its relations strained with South Korea ― all of which have sought support from Washington, long the pre-eminent naval power in Asia.

Xinhua said refitting and test work would continue on the carrier when it returns from its short sea trial.

The Varyag, yet to be officially renamed, was towed from Ukraine as an empty shell without engines, weapons systems or other crucial equipment.

Defense experts say China plans up to four carriers in all, with preparations under way at a Shanghai shipyard.

The Xinhua report did not say how long the sea trial would last. But a statement posted on the website of the Liaoning Maritime Safety Authority said “all vessels will be barred from entering” a small section of the sea off Dalian until 6 p.m. on Sunday.

There had been earlier online reports in China that the test was set to start last weekend, but it may have been delayed by a tropical storm that swept through the area.