The US and Russian militaries are blaming each other after their warships came within 50m, with both sides claiming they were forced to perform emergency manoeuvres.

In what appears to be a game of brinkmanship on the high seas, the navies were involved in a near-collision with two huge vessels coming into extreme close proximity.

Russia’s Pacific Fleet claims the guided-missile cruiser USS Chancellorsville crossed just 50m in front of its destroyer Admiral Vinogradov in the East China Sea.

But the US claims the incident occurred in the Philippine Sea and has dismissed the Russian assertion as “propaganda”, saying the Russians made an “unsafe manoeuvre” against the Americans.

Video of the incident obtained by CNN and taken from the US cruiser, shows the two vessels veering so close that Russian soldiers are visible on the stern.

The US said it would lodge a formal diplomatic complaint over the Russian warship’s movements.

The US 7th Fleet said the Russian destroyer put the safety of the USS Chancellorsville and its crew at risk on Friday, forcing it to reverse all engines at full throttle to avoid a collision.

It said a helicopter was preparing to land on the Chancellorsville when the Russian destroyer, travelling behind the US ship, sped up and got as close as 15 to 30m.

US 7th Fleet spokesman Clay Doss said no one was injured and he wasn’t aware of any damage to the ship.

“We consider Russia’s actions during this interaction as unsafe and unprofessional and not in accordance with the International Regulations for Preventing Collisions at Sea (COLREGS), ‘Rules of the Road,’ and internationally recognised maritime customs,” the 7th Fleet said in a statement.

But the Russian military accused the Chancellorsville of making a dangerous manoeuvre by crossing the path of the Russian destroyer Admiral Vinogradov.

It said in a statement that the US cruiser “suddenly changed direction and crossed the path of Admiral Vinogradov just 50 metres (165 feet) away,” forcing the crew of the Russian ship to make a quick manoeuvre to avoid collision.

The Russian military said its navy sent a radio message in protest.

With US-Russian relations at post-Cold War lows, the Russian and US militaries have frequently exchanged accusations of what they describe as unsafe manoeuvres by the other side’s warplanes and navy ships.

On Tuesday, the US accused Russia of intercepting a US aircraft flying in international airspace over the Mediterranean Sea.

The warship incident comes amid US and Moscow tensions over a range of issues including Russian interference in the 2016 presidential election, and at a time of greater co-operation between China and Russia.

-with AAP