BEIJING — China’s first domestically built aircraft carrier slipped into the sea for the first time on Wednesday, after days of publicity celebrating the impending launch as a milestone in President Xi Jinping’s drive to extend China’s military reach far beyond its shores.

Senior military and government officials watched as a champagne bottle was smashed on the bow and as the 1,033-foot gray hull of the carrier eased into the water at Dalian, a northeastern port, the Chinese military news media reported. The ship, festooned with red national flags and banners, then stopped next to the dock.

The launch “signified a major stage of progress of our country’s indigenous design and construction of aircraft carriers,” a news bulletin from the People’s Liberation Army said. It said the carrier would undergo more testing and fitting of equipment before trials in the water.

The carrier launch comes as tensions rise over China’s activities in the South China Sea and North Korean’s nuclear ambitions. China is entangled in maritime disputes with several Asian countries, including Japan, the Philippines and Vietnam. India is also wary of China’s growing presence in the Indian Ocean, and Australia is responding to China’s naval buildup with its own.