The tariffs, if implemented, could dramatically raise prices for American consumers on everything from gas to automobiles to agricultural products.

Mexico and Canada are the United States’ top two trading partners, accounting for nearly 30% of trade volumes.

Mexico has supplanted China as the main source of goods, but imports keep climbing.

The president-elect said that he would impose the across-the-board tariffs on Day 1 and that they would stay in place until Canada, Mexico and China halted the flow of drugs and migrants.

Trump, who takes office on Jan. 20, said he would impose a 25% tariff on imports from Canada and Mexico until they clamped down on drugs, particularly fentanyl, and migrants crossing the border, in a move that would appear to violate a free-trade deal.

Chinese firms are on edge and so are some of their US partners. Markets are relatively muted, though the yuan is down.

President-elect Trump’s emphatic promise of new tariffs is sharpening the debate over how he will handle the economy. It’s likely the single most important domestic issue of his second term. Trump is poised to enjoy almost perfect timing in taking the reins of an economy on the rise.

By Joe Cash BEIJING (Reuters) -China attacked U.S. President-elect Donald Trump's pledge to slap additional tariffs on Chinese goods over fentanyl flows, saying his incoming administration was pushing the blame for America's opioid crisis onto China.