Russia launched Tuesday what it called its largest ever military drills, with hundreds of thousands of troops taking part along with Chinese soldiers in a show of force Nato condemned as a rehearsal for "large-scale conflict."
President Vladimir Putin is expected to attend the games after hosting an economic forum in Russia's far eastern city Vladivostok where his Chinese counterpart Xi Jinping is one of the prominent guests.
The week-long war games dubbed "Vostok-2018"(East-2018) "have kicked off" in far eastern Russia, the defence ministry said.
Taking part in the drills are around 300,000 soldiers, 36,000 military vehicles, 80 ships and 1,000 aircraft, helicopters and drones.
Some 3,500 Chinese troops will take part in the exercise.
The defence ministry released video footage of military vehicles, planes, helicopters and ships getting into position for the initial stage of the drills.
Putin praised Russia's increasingly close ties with China as he met Xi at the economic forum in Vladivostok on Tuesday.
"We have trustworthy ties in political, security and defence spheres," the Russian leader said.
Xi for his part said the two countries' "friendship is getting stronger all the time."
The drills, which also include Mongolian soldiers, have been condemned by NATO as a rehearsal for "large-scale conflict".
The military exercises come at a time of escalating tensions between Moscow and the West over accusations of Russian interference in western affairs and conflicts in Ukraine and Syria.
The Russian army has compared the show of force to the USSR's 1981 war games that 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 are 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," Shoigu 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.
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 games featuring anti-aircraft technology, while the main event will be on Thursday, the defence ministry told journalists covering the event in eastern Siberia and the Far East.
NATO said that 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," the alliance's spokesman Dylan White said late August.
Separately, US Defence Secretary Jim Mattis downplayed the significance of China's participation.
"I think that nations act out of their interests. I see little in the long term that aligns Russia and China," he said.
Putin's spokesman Dmitry Peskov dismissed western concerns on Tuesday.
"These are very important drills but they are part of routine annual work to develop the armed forces," he told journalists.
Peskov has 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 the outbreak of 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 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 participating.
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.