Chinese and Russian naval forces have begun six days of joint exercises in the Yellow Sea off China's eastern coast, Chinese state media report.
Anti-submarine operations and the simulated rescue of hijacked vessels will feature in the drills.
It is first time the two navies have conducted such drills, although both countries have participated in four military exercises since 2005.
They come amid tensions with China's neighbours over territorial claims.
Six countries claim competing sovereignty over areas in the South China Sea, which is believed to contain huge deposits of oil and gas.
That has led to occasional flare-ups and competition to occupy islands, reefs and sandbars. Last week the US and Philippines began joint military exercises in the South China Sea.
China said on Thursday that these drills were aimed at upholding regional peace and some analysts say they are also a sign of closer ties between the regional giants.
"This joint military exercise is a long scheduled one between China and Russia in order to uphold regional peace and stability," AFP quotes foreign ministry spokesman Liu Weimin as saying.
More than 4,000 Chinese service personnel will attend and China will also supply 16 vessels made up of five missile destroyers, five missile frigates, four missile boats and a support vessel and hospital ship.
Thirteen aircraft and five shipboard helicopters will also take part, Xinhua reports.
Russia's contribution includes four warships, three of them missile cruisers, and three supply ships, Xinhua adds.
The exercises will focus on joint maritime air defence, anti-submarine tactics, maritime search and rescue as well as efforts to rescue hijacked vessels, Chinese security officials say.----
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