Thousands of Russian troops joined Chinese soldiers in a show of force on Tuesday which Nato described as a rehearsal for "large-scale conflict".
President Vladimir Putin is expected to attend what Russia called its largest ever military drill after hosting an economic forum in Vladivostok where his Chinese counterpart Xi Jinping is a prominent guest.
The week-long Vostok-2018 (East-2018) war games "kicked off" in far eastern Russia, the Defence Ministry said.
About 300,000 soldiers, 36,000 military vehicles, 80 ships and 1,000 aircraft, helicopters and drones are taking part.
Also involved are about 3,500 Chinese troops.
The Russian Defence Ministry released footage of military vehicles, planes, helicopters and ships moving into position for the initial stage of the drills.
Mr Putin praised Russia's increasingly close ties with China as he met Mr Xi.
"We have trustworthy ties in political, security and defence spheres," the Russian leader said.
Mr Xi said the two countries' "friendship is getting stronger all the time".
The military exercises come amid escalating tensions between Moscow and the West over accusations of Russian interference and conflicts in Ukraine and Syria.
The Russian army compared the show of force to the Soviet Union's 1981 war games which saw between 100,000 and 150,000 Warsaw Pact soldiers take part in Zapad-81 (West-81) - the largest military exercises of the Soviet era.
But Defence Minister Sergei Shoigu said these exercises were even larger.
"Imagine 36,000 military vehicles moving at the same time: tanks, armoured personnel carriers, infantry fighting vehicles - and all of this, of course, in conditions as close to a combat situation as possible," he said.
The exercises will be held across nine training ranges and three seas: the Sea of Japan, the Bering Sea and the Sea of Okhotsk.
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The Russian army is rolling out all of its latest additions for the event: Iskander missiles that can carry nuclear warheads, T-80 and T-90 tanks and its recent Su-34 and Su-35 fighter planes.
At sea, the Russian fleet is deploying several frigates equipped with Kalibr missiles that have been used in Syria.
Wednesday will see drills featuring anti-aircraft technology, while the main event will be on Thursday, the defence ministry said.
Nato said Vostok-2018 "demonstrates Russia's focus on exercising large-scale conflict".
"It fits into a pattern we have seen over some time - a more assertive Russia, significantly increasing its defence budget and its military presence," spokesman Dylan White said.
Mr Putin's spokesman Dmitry Peskov dismissed such concerns on Tuesday.
"These are very important drills but they are part of routine annual work to develop the armed forces," he said.
Mr Peskov earlier said Russia's "ability to defend itself in the current international situation, which is often aggressive and unfriendly to our country, is justified, essential and without alternative".
Relations between Russia and the West declined sharply in 2014 with Moscow's annexation of Crimea and a Kremlin-backed uprising in eastern Ukraine.
The Kremlin has accused Nato of expanding westwards and threatening Russian national security.
Moscow has increased the number of its large-scale military exercises in the Caucasus, the Baltic region and the Arctic in recent years.
Russia's previous military exercise in the region, Vostok-2014, was almost half the size, with 155,000 soldiers taking part.
The country's war games in Eastern Europe last year, Zapad-2017, saw 12,700 troops take part, according to Moscow. Ukraine and the Baltic states said the true number was far bigger.
