President Donald Trump says the long-threatened 25% US tariffs against Canada and Mexico will kick in from today Tuesday March 4.

Trump has said the import taxes will force the US neighbours to take more action to curb illegal drugs and migrants entering the country.

A 10% tariff on Chinese imports is also expected, be in addition to tariffs Trump imposed last month and bring levies on Chinese goods to 20%, in response to accusations that Beijing is not doing enough to stop the flow of fentanyl into the US.

All three countries, Canada, China and Mexico, have said they will retaliate against the US in response to the tariffs, raising the prospect of a widening trade war