Ties between Moscow and Beijing have grown closer since Russia invaded Ukraine last year, a move China has not condemned.

The two have ramped up defence contacts, including joint military drills in recent months.

The latest air-and-sea exercises will take place in the Sea of Japan and are aimed at "safeguarding strategic maritime routes", the Chinese Ministry of Defence had said Saturday.

The Chinese military has sent five warships, including a guided-missile destroyer, it added in the statement published Sunday, without specifying when the drills will take place.

China and Russia carried out a joint air patrol over the Seas of Japan and East China last month, and the flights prompted South Korea to deploy fighter jets as a precaution.

It was the sixth such China-Russia patrol in the area since 2019.

China's defence minister Li Shangfu this month advocated boosting naval cooperation with Russia.

Beijing has emerged as Moscow's most important ally since the Ukraine war began.

China says it is a neutral party in the conflict but its refusal to condemn the invasion has led to accusations from Ukraine's allies that it is favouring Russia.