US President Donald Trump has announced that 25% tariffs on goods from Mexico and Canada will come into effect today - causing global market panic and leaving the countries scrambling to retaliate.

       The US will now tax imports from Mexico and Canada at 25% and double tariffs against China to 20% after the changes came into effect at around midnight local time. Canadian energy products will be subject to a reduced levy of 10%.

       Trump announced his intention to bring in the hefty levies against the countries at the beginning of the year, but put them on the backburner after his some of his demands around stopping drug trafficking and illegal immigration were met.

       But, in an address at the White House on Monday, the president said time had run out for pre-tariff negotiations with Canada and Mexico, two of the US's biggest trading partners.

       “[Tariffs are] a very powerful weapon that politicians haven’t used because they were either dishonest, stupid or paid off in some other form,” Trump said.

       “And now we’re using them.”

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       Canada and China have already announced retaliatory tariffs of their own, with Canadian Prime Minister Justin Trudeau pledging to introduce tariffs on more than 100 billion dollars (￡78.7 billion) of American goods in the next 21 days.

       In response to further levies on Chinese imports, Xi Jinping also announced the country would impose new tariffs of up to 15% on US farming imports including chicken, pork, soy and beef.

       Trump has said the reason for tariffs on Mexican and Canadian goods is to address the issue of drug trafficking and illegal immigration, as well as a trade imbalance with the US.

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       Despite the introduction of new tariffs against key trading partners causing a dip in the US stock market, Trump's administration has remained adamant that his approach is the right one to promote US manufacturing and attract foreign investment.

       Tariffs were a central component of the economic plan Trump laid out during his election campaign, during which he claimed it was his favourite word.

       While the repercussions of the Mexican, Canadian and Chinese tariffs on the US economy have yet to be seen - with the administration rebuffing claims that they could increase inflation and stoke trade wars - Trump has also pledged to take action against the European Union and India, on an unspecified timescale.

       Sir Keir Starmer sought to flesh out a trade deal between the UK and the US during his visit last week, in a bid to minimise the fallout of the drastic taxation on non-EU Britain.