A US federal court has blocked President Donald Trump's sweeping tariffs, in a major blow to a key part of his economic plan.

The Court of International Trade ruled that an emergency law invoked by the White House does not give the president unilateral authority to impose tariffs on nearly every country.

The Manhattan-based court said the US Constitution gives Congress exclusive powers to regulate commerce with other nations and this is not superseded by the president's remit to safeguard the economy.

The court also blocked a separate set of levies the Trump administration imposed on China, Mexico and Canada, which were in response to what the White House said was the unacceptable flow of drugs and illegal immigrants into the US.

Steel and aluminium tariffs are not affected, as they fall under a different law.

How the White House reacted: "It is not for unelected judges to decide how to properly address a national emergency," the White House said as it launched an appeal against the ruling.

The ruling gave the White House 10 days to complete the bureaucratic process of halting the tariffs, although most are currently suspended anyway.

The immediate implications of the court's ruling are unclear. The case needs to go through the appeals process - a higher court might be more Trump-friendly.

(Source: BBC)