The two countries have drawn closer in recent years and share hostile relations with the US-led defence alliance NATO, which last week called an infuriated China a "decisive enabler" of Russia's invasion of Ukraine.

Beijing and Moscow both said last week that they were conducting joint drills known as Joint Sea-2024 off the coast of Zhanjiang, a city in southern China's Guangdong province.

The area is part of the South China Sea, much of which Beijing claims to the chagrin of other littoral states.

The Chinese navy said in an online statement Thursday that both sides had "completed all designated projects and exercises" by Wednesday afternoon.

Seven warships took part in the six-day drills aimed at "jointly responding to maritime security threats", the navy said.

The drills "strengthened professional exchanges, mutual understanding and trust between the Chinese and Russian navies (and) promoted the standardisation and systemisation of... bilateral practical cooperation", the navy added.

It published photos of grey battleships sailing in two lines across a stretch of azure ocean before turning off in different directions as part of a farewell ceremony.

Longtime socialist allies with historically tempestuous ties, China and Russia have recently touted their friendship as having "no limits", embodied by the supposed bonhomie between presidents Xi Jinping and Vladimir Putin.

Beijing has refused to condemn Moscow's invasion of Ukraine, insisting it is a neutral party in the conflict while strengthening diplomatic, economic and military ties with its vast northern neighbour.

At a summit in Washington this month, NATO leaders said the two countries' partnership and Beijing's "large-scale support for Russia's defence industrial base" were a cause of "profound concern".

China swiftly hit back by accusing NATO of "hyping up the so-called China threat and provoking confrontation and rivalry", defending Beijing's position on Ukraine as "open and above board".

In a separate statement on Sunday, China's defence ministry said it had conducted joint naval patrols with Russia in the northern and western Pacific, adding that the exercise was not "targeted" at any other nation.