Donald Trump pressed a hidden five-tap code into his handshake with Xi Jinping, a body language expert has revealed, as the two leaders met in Beijing. 

The President arrived to a full imperial welcome on Thursday, his motorcade sweeping into Tiananmen Square decked out with goose-stepping troops and thundering cannon fire.

Body language expert Judi James told the Daily Mail the handshake revealed the real power dynamics at play, with Trump also betraying himself the instant he locked eyes with Xi through a giveaway 'bullfrog smile'. 

Trump then made the opening move, James said, despite Xi being the host.

'It was Trump instigating the handshake by throwing his own hand out, palm tilted upward, from a few paces away. The one instigating the shake gets an early sense of dominance, which is why it is usually the host,' James said.

The pair gripped each other's hands for a full ten seconds, with Trump giving Xi a sequence of small, deliberate pats that James said carried diplomatic weight. 

'When the hands are juddering together Trump pats Xi's hand, twice at first, then three times with the first of the third pats being prolonged in a move that suggests a desire to cement the relationship,' James said. 

Yet the mood, she added, was nothing like the warmth on display when Vladimir Putin visited China last year. 

'Trump used strong, enquiring-looking eye contact as they engaged in some chat ... with none of the joking, animated playfulness that we saw during Putin's visit,' she said.

It is Trump's first face-to-face with Xi since the Iran war erupted on February 28, sending global oil prices skyrocketing.

The formality thawed as flag-waving children greeted Trump, who broke into a grin and applauded them.

'He then began to use a series of approval, bonding pats on Xi's arm as they walked together to increase the idea of friendship,' James said.

Inside the Great Hall, Xi opened the talks with an ominous reference to the so-called Thucydides Trap, the ancient Greek historian's account of Athens and Sparta, and the danger when an established power feels threatened by a rising civilization.

'The world has come to a new crossroads. Can China and the US overcome the Thucydides Trap and create a new paradigm?' Xi asked Trump across the table.

During their two-hour summit, Xi warned Trump that if Taiwan is 'mishandled' the US and China 'will clash, or even come into conflict, pushing the entire relationship into a very dangerous situation,' state media channel CCTV reported. 

Trump was effusive before the closed-door summit got underway, praising the pageantry of his welcome as 'an honor like few have ever seen before.'

'It's an honor to be with you, it's an honor to be your friend, and the relationship between China and the USA is going to be better than ever before,' he told Xi. 

The setting for their grand summit told its own story, James said.

'The meeting room was huge but the layout of the tables was actually relatively intimate by normal Chinese government standards, suggesting a desire from Xi to indulge in more direct and functional face-to-face discussions,' she added.

Trump's posture once seated revealed his game face, according to James.

'Trump adopted a pose of a relaxed but serious heavyweight alpha at the table, sitting hunched forward with his hands hidden beneath the table,' she said. 

The visit was originally slated for March but was postponed when the war broke out.