US President Donald Trump has confirmed that a new round of tariffs on Beijing will go into effect on Sunday in the latest tit-for-tat of the US trade war with China.

China tariffs are “on,” the president told reporters before departing to Camp David, the presidential retreat on Friday.

“A lot of companies have left China and a lot more are leaving,” the president said without providing any evidence.

The US is planning to impose 15 per cent tariffs on $US300 billion ($445 billion) worth of Chinese goods.

Some of that will start in September and another tranche in December, in order, the president says, to avoid harm to consumers ahead of Christmas.

Earlier this month China announced plans to impose tariffs on an additional $US75 billion ($111 billion) worth of US goods imported into the country, and Mr Trump responded by increasing the September tariffs from 10 to 15 per cent.

The moves are the latest in a year-long trade war that is slowing the world economy.

Washington has already slapped tariffs on $US250 billion worth of Chinese goods, to which China has retaliated with duties on $US110 billion worth of US imports.