President Donald Trump said the sweeping tariffs that he has imposed on Mexico, Canada and China may cause "short term" pain for Americans as global markets reflected concerns the levies could undermine growth and reignite inflation.

Amid warnings of price increases, Canada moved quickly to retaliate, China said it had planned countermeasures and Mexico said it would soon unveil its response.

The tariffs were also pushed through despite the terms agreed between the U.S., Canada and Mexico in the U.S.-Canada-Mexico Agreement, negotiated by Trump in his first term, after he pledged to get rid of the North American Free Trade Act (NAFTA) negotiated by President Bill Clinton.