Beijing rejected the warnings as "irresponsible and provocative," hours after China's defence ministry said the two militaries had begun the exercises -- called Joint Sea-2024 -- in "early July," lasting until the middle of this month.

The drills in the waters and airspace around Zhanjiang, a city in southern Guangdong province, are "to demonstrate the resolve and capabilities of the two sides in jointly addressing maritime security threats and preserving global and regional peace and stability", the ministry said.

It added that the exercises "will further deepen China-Russia comprehensive strategic partnership of coordination for the new era".

They were taking place in accordance with Beijing and Moscow's annual plan for military engagement, according to the ministry.

The announcement came in the same week that NATO leaders convened in Washington to reaffirm support for Ukraine amid Russia's invasion.

China and Russia have drawn closer in recent years and tout their friendship as having "no limits", and both share hostile relations with NATO.

NATO leaders said in a declaration on Wednesday that China had "become a decisive enabler" of Moscow's invasion of Ukraine, prompting Beijing to warn NATO against "provoking confrontation".

Beijing "strongly condemns the irresponsible and provocative remarks made by the NATO Secretary General against China, which are steeped in Cold War mentality and ideological bias, and consist of baseless accusations," a foreign ministry spokesman said Friday, according to Xinhua.

China maintains that it is not a party to the Ukraine conflict but has been criticised by Western leaders for giving political and economic support to Russia, including in the trade of goods with both civilian and military uses.

Chinese forces are also staging drills this week with Belarus, another Russian ally, on NATO's eastern border.

Japan said Friday that joint China-Russia activities near its territory pose a "grave concern from the perspective of national security".