Nancy Pelosi, the highest-ranking woman in the history of US politics, was re-elected on Wednesday to lead congressional Democrats, a major step on her march toward once again becoming speaker of the House of Representatives.

World leaders began arriving in Argentina ahead of a G20 summit dogged by increasingly strident warnings about the impact on the world economy of threatened US trade tariffs.

The UN Commission of Inquiry on Syria has urged the Security Council to press the Syrian government to provide information to families about the fate of those missing or detained during the seven-year war.

British Prime Minister Theresa May will argue on Wednesday that she managed to secure broader fishing rights for Scotland in the face of firm EU opposition in tough Brexit talks.

An explosion and fire near a chemical factory left at least 22 people dead and 22 others injured on Wednesday in a northern China region that will host the 2022 Winter Olympics, authorities said.

Flights were cancelled, railway lines closed and motorists stranded on flooded roads, as a month's worth of rain fell on Sydney early on Wednesday, leaving emergency services battling to respond.

Ukrainian President Petro Poroshenko on Tuesday warned of the threat of "full-scale war" and said Russia had sharply increased its military presence on their shared border as tensions escalate between the ex-Soviet neighbours.

US President Donald Trump said Monday he expected to raise the punitive tariff rates on hundreds of billions in Chinese imports as scheduled next year.

Beijing has ordered an investigation into claims by a Chinese scientist to have created the world's first genetically-edited babies, a move that would be a ground-breaking medical first but which has generated a barrage of criticism.