US President Donald Trump is threatening to double the 10 percent tariff on goods from China next week, if it does not do more to combat fentanyl trafficking.

Trump told reporters on Thursday at the White House that China "should not be allowing those drugs to come into the United States of America, and we're not going to allow it to happen."

This followed his announcement about the new tax on social media earlier in the day. It will take effect March 4, and it is on top of another 10 percent he imposed earlier this month.

He accused China of supplying a large amount of the fentanyl that flows into the US. He said this needs to be stopped or "seriously limited."

The president also said that the 25 percent levies on Mexican and Canadian goods will also start the same day, as planned. Those tariffs had been paused for a month. He blames his neighbors for the drug flowing across the borders.

Trump also said "reciprocal tariffs" on all trading partners will start, as scheduled, on April 2.