California sues US government over Trump tariffs

California is suing the federal government over Donald Trump's on-again-off-again tariffs, the governor and attorney general said Wednesday, claiming the American president does not have the right to impose them.

The move marks the strongest pushback yet against a tariff roll-out that has sent global stock markets into meltdown, and left businesses across the US fretting about uncertainty.

"It's the worst own-goal in the history of this country," California Governor Gavin Newsom said.