US President Donald Trump lashed out in unusually personal terms against the six Supreme Court justices who handed him one of the biggest setbacks of his second term in office by striking down the administration's global tariffs.

The court's Friday ruling was "deeply disappointing". The justices who joined the majority opinion should be "absolutely ashamed" and lacked the courage to "do the right thing", Trump said, turning his response into a sweeping attack against a co-equal branch of government.

The broadside was remarkable even for a president known for blowing past political norms and publicly berating those who challenge his authority.

"I'm ashamed of certain members of the court. Absolutely ashamed for not having the courage to do what's right for our country," Trump said at the start of a press conference at the White House, which was held a few hours after the decision was released.

Trump did not mince words from there as he assessed the decision, which held that presidents do not have inherent authority to impose sweeping tariffs on any country.

For the next 45 minutes, Trump criticised the ruling and made the case that he would find other methods to continue imposing tariffs on other countries. But throughout he repeatedly returned to the justices in ways that made clear he felt personally slighted by the decision.

The president did not discriminate against Republican and Democratic appointees, either.

The six justices who struck down Trump's tariffs were equally divided among the court's liberal and conservative wings. Three - Justices Elena Kagan, Sonia Sotomayor and Ketanji Brown Jackson - were appointed by Democratic presidents. The other three were appointed by Republicans. Chief Justice John Roberts is a George W Bush pick who wrote the majority opinion, and Justices Neil Gorsuch and Amy Coney Barrett were appointed by Trump in his first term in office. Trump went after them all.