China and Canada retaliate after Trump trade tariffs come into effect

China and Canada unveiled retaliatory measures against the US after Donald Trump imposed his sweeping tariffs plan at midnight US time, despite warnings it could spark an escalating trade war. US tariffs have come into force of 25% against goods from Canada and Mexico, the US's two biggest trading partners, and 20% tariffs against China - doubling the levy on China from last month. The duties stand to affect over $918bn worth of US imports from Canada and Mexico. China on Tuesday said it would impose fresh tariffs on a range of agricultural imports from the US next week. Its…