Russia has launched its biggest military exercise since the Cold War, involving about 300,000 service personnel, in eastern Siberia.
China is sending 3,200 troops to take part in “Vostok-2018”, with many Chinese armoured vehicles and aircraft. Mongolia is also sending some units.
The last Russian exercise of similar scale was in 1981, during the Cold War, but Vostok-2018 involves more troops.
The week-long manoeuvres come at a time of heightened Nato-Russia tensions.
As the exercises began, Russian President Vladimir Putin met his Chinese counterpart Xi Jinping at a forum in the eastern city of Vladivostok and told him “we have a trusting relationship in the sphere of politics, security and defence”.
Relations between Russia and Nato – a 29-member defence alliance dominated by the US – have worsened since Russia annexed Crimea from Ukraine in 2014.