HAMBURG: US President Donald Trump meets Russian leader Vladimir Putin for the first time Friday, in an eagerly awaited encounter at a G20 summit marked by the growing divide between America and its Western allies.

On the eve of a face-off that carries consequences for world crises including the wars in Syria and Ukraine, Trump set the tone Thursday with a strong attack against Moscow for its "destabilising" actions.

The property tycoon and the ex-KGB agent's first meeting promises to be dissected frame by frame, with their handshake and body language including each facial twitch to be scrutinised for any sign of rapprochement or estrangement.

"While Trump pro-wrestling approach is showy, bombastic and impulsive, Putin thrives on judo's discipline and mental toughness, where a core technique is to keep an opponent off-balance and exploit his weakness," noted Derek Chollet from think-tank German Marshall Fund.

"How these contrasting styles of machismo interact... will likely be the defining feature of their relationship moving forward."

The blockbuster bilateral meeting comes on the sidelines of what is expected to be the most fraught G20 summit in years in the German city of Hamburg.

Trump's "America First" and climate skeptic stance are set to test the relationship with longstanding allies, while North Korea adds more volatility to global security.

Scenes outside the heavily guarded conference hall were also stormy, as anti-globalisation protesters fought running battles overnight with police who fired tear gas and used water cannon to disperse extreme-left Black Bloc militants late Thursday.