BEIJING (AP) — China has closed off a swath of ocean off its east coast for military activities, but has said little about what the exercises entail.

A notice from the government of the eastern port city of Lianyungang says a roughly 40,000-square-kilometer (15,000-square-mile) section of the Yellow Sea was off-limits to commercial shipping from Thursday through Saturday.

The notice sourced to the People's Liberation Army says only that "large-scale military activities" are being held between Lianyungang in Jiangsu province and the Shandong province port of Qingdao that is home to the navy's North Sea Fleet.

The exercises come days ahead of commemorations of the PLA's 90th anniversary, specifics of which have not yet been announced.

China has lately stepped-up navy exercises conducted further from home ports, including those involving its sole operating aircraft carrier and its battle group. On Thursday, the Chinese and Russian navies were wrapping up an initial set of drills in the Baltic Sea near St. Petersburg.

The eight-day "Joint Sea 2017" exercises include the Chinese missile destroyer Hefei and missile frigate Yuncheng and were focused on joint rescue missions and "ensuring maritime economic activities," China's official Xinhua News Agency reported.