China's President Xi Jinping warns against 'empty talk' as G20 summit opens

Leaders of the world's biggest powers met on Sunday to try to revive the sluggish world economy, with their host Chinese President Xi Jinping urging them to avoid "empty talk". Xi welcomed each president and prime minister to the Group of 20 summit with a handshake and had an extended clasp with Barack Obama, with both men smiling despite protocol stumbles around the US leader's visit.

In a circular conference hall in Hangzhou -- the scenic eastern city left deserted by a vast security operation -- Xi told them the G20 "should work with real action, with no empty talk".

China is hoping a successful meeting will portray it as an assured and powerful nation ready to assume a role on the international stage that befits its status as the world's second-largest economy.

Authorities shut thousands of factories to try to clear the skies of smog, and encouraged residents to leave town on free holidays, as well as detaining dozens of dissidents to prevent any hint of unrest.

The G20 brings together representatives of 85 percent of the world's GDP and two-thirds of its population. But experts expect the gathering to be short on substance, with no acute crisis pushing leaders to defy rising populist sentiment and to take difficult steps such as liberalising trade.

Xi said the global economy "still faces multiple risks and challenges including a lack of growth momentum and consumption, turbulent financial markets, receding global trade and investment".

"We hope the Hangzhou summit will come up with a prescription for the world economy and lead it back to the road of strong, balanced, comprehensive and sustainable growth." The summit was preceded by a flurry of diplomatic activity on issues ranging from climate change and the war in Syria to international trade.

The US and China on Saturday ratified the Paris climate accord, a crucial step towards bringing into force the pact against global warming. UN chief Ban Ki-moon, who personally received the ratification documents from Xi and Obama, applauded them today for "making this historic step" and urged other G20 leaders to follow suit.

There had been hopes for another breakthrough, on the long war in Syria, after the US said it was close to a deal with Russia on stemming the violence.