China's first aircraft carrier began sea trials Wednesday, marking a milestone in the country's rapid military modernization and long-term strategy to challenge U.S. military supremacy in Asia and project power far beyond Chinese shores. The 300-meter-long carrier, based on an empty hull bought from Ukraine, sounded its horn three times as it ploughed through the morning fog around Dalian and headed out to sea, according to one witness writing on the military microblog of the state-run Xinhua news agency. The carrier, featuring its original ski-jump runway to launch fighters and a new engine and radar equipment, has been undergoing refurbishment for the past decade in the northeastern port. Xinhua said the sea trials "would not take a long time," without giving details of the exact duration or say what sort of tests would be carried out. "After returning from the sea trial, the aircraft carrier will continue refit and test work," it said. The provincial Maritime Safety Authority said on its web site that "all vessels will be barred from entering" a small section of sea off Dalian until 6 p.m. local time Aug. 14.