LOS ANGELES: California is suing the federal government over Donald Trump's on-again-off-again tariffs, the governor and attorney general said on Wednesday (Apr 16), 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. "One of the most self-destructive things that we've experienced in modern American history."

With 40 million people and a large, outward-facing economy that accounts for 14 per cent of US GDP, California looks set to bear the brunt of the economic damage forecasters expect from recent gyrations.

Newsom's office says California - which would be the world's fifth-largest economy if it were an independent country - could lose billions of dollars in revenue if Trump's tariff policies shrink international trade.

Trump has long prized tariffs as a tool to achieve what he says is the urgent task of rebalancing America's trading relationships, and pledged on the campaign trail that he would hit imports with extra levies.

Initial punitive tariffs against Mexico and Canada were built on with his self-declared "Liberation Day", which saw onerous charges imposed on scores of countries, including allies and partners.

Many of those duties have since been paused, but their chaotic announcement sent global stock markets into spasms, wiping out trillions of dollars of value.

Newsom said Trump's economic mismanagement was costing everyday Americans - including many who voted for Trump - dearly, all while feathering the nests of billionaire donors and friends.

The United States, he said, has gone in a matter of weeks "from free capitalism to crony capitalism, just like that".

"This is the personification of corruption ... this is smash-mouth, in-your-face, every minute of every day, every hour.

"How in the hell are we sitting by and allowing this to happen?" said Newsom, who is widely expected to put himself forward as a candidate for the presidency in 2028.

The legal action launched on Wednesday argues that the International Emergency Economic Powers Act, which Trump has used to impose levies as high as 145 per cent, does not grant him the authority to put tariffs on goods coming into the US.

"We're asking the court to rein in the president ... and uphold the Constitution," Attorney General Rob Bonta told reporters.

"The president is yet again acting as if he's above the law, he isn't."

Bonta said the power to impose tariffs rests with Congress, and the suit sought to ensure his actions were rolled back.

"It's simple, Trump does not have the authority to impose these tariffs. He must be stopped."

The case is the latest of more than a dozen lawsuits that California has filed against the Trump administration.

A White House spokesman quoted by local media dismissed the lawsuit.

"Instead of focusing on California's rampant crime, homelessness, and unaffordability, Gavin Newsom is spending his time trying to block President Trump's historic efforts to finally address the national emergency of our country's persistent goods trade deficits," the spokesman said.

California sues US government over Trump tariffs