US President Donald Trump has instructed aides to proceed with tariffs on about $200 billion more of Chinese products, a source familiar with the process said on Friday, adding that the timing is not yet clear.

An earlier Bloomberg report on Friday that Trump was moving ahead on the tariffs despite Treasury Secretary Steven Mnuchin's attempts to restart talks with China on resolving the trade war had an immediate effect on financial markets, leading US stocks to reverse course and trade lower.

The step comes one week after Trump raised the possibility of duties on the $200 billion of imports and also threatened tariffs on another $267 billion worth of goods. Trump has already levied duties on $50 billion worth of Chinese goods.

The United States only imported $505 billion in goods imported from China last year. But 2018 imports from China through July were up nearly 9 per cent over the same period of 2017, according to US Census Bureau data.

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