US President Donald Trump's tariffs on its biggest trading partners- China, Mexico, Canada- came into effect on Tuesday. China, hit by 20% tariffs, announced 10%-15% tariffs on various US imports from March 10. Canada announced 25% reciprocal (equivalent) taxes on $20.7-billion US imports. Mexico, also hit with 25% tariffs, said contingency plans were in place, but its response is awaited.