Washington DC - A handful of Senate Republicans broke ranks with President Donald Trump on Wednesday, joining Democrats to pass a measure that would block his tariffs on Canadian imports.

The resolution, supported by four Republicans and all of the chamber's Democrats, has virtually no chance of becoming law.

But it marks a rare, albeit symbolic defeat for Trump on Capitol Hill, where his Republican Party controls both chambers and he has seen little pushback to his rampaging first months in office.

The Senate voted 51-48 to overturn the national emergency at the border which Trump declared earlier this year, which he has used to justify saddling Canadian imports with 25% tariffs.

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But it was a purely symbolic dissent, as House Speaker Mike Johnson, a close Trump ally, is expected to block any vote on the resolution.

Trump took to his Truth Social media platform to slam the legislation as a Democratic "ploy" and make clear it is dead on arrival in the House.

"The House will never approve it and I, as your President, will never sign it," he posted.

The four Republican senators who voted to pass the measure were Lisa Murkowski of Alaska and Susan Collins of Maine – viewed as the two most-centrist party members – as well as Kentucky's two senators, Mitch McConnell and Rand Paul.

Republicans have a 53-47 majority in the Senate.

The Senate vote occurred shortly after Trump rolled out his plans to slap fresh import tariffs on products from countries around the globe, an announcement that sent stock markets tumbling.