The number missed analysts' forecasts that shipments from the world's largest exporter would rise 10.1 percent, slowing only slightly from 12.2 percent in July.
The two sides launched another salvo on August 23, imposing duties on United States dollars 16 billion worth of products from each country.
If the president follows through, the threatened tariffs and those already in place would more than cover the value of all goods the USA buys from China, according to United States government data from previous year.
Chinese exports to the United States rose to US$44.4 billion in August, a 13.2 per cent increase from the same period a year ago, according to customs data.
The Trump administration has offered aid to farmers impacted by the retaliatory trade moves, which include tariffs on US crops like soy beans. But if Trump adds the $200 billion in Chinese products to the target list, American consumers would likely feel the pinch directly.
China's imports from the United States grew only 2.7 percent in August, a slowdown from 11.1 percent in July.
"And I hate to say that, but behind that, there's another US$267 billion ready to go on short notice if I want". "That totally changes the equation".
Cell phones are the biggest USA import from China, and so far they've been spared.
Navarro said the administration would "love to have a fair relationship with China", the world's second-largest economy.
White House Economic advisor Larry Kudlow told CNBC that talks between the USA and China were ongoing. Those tactics, the Office of the US Trade Representative has alleged, include stealing trade secrets through computer hacking and forcing US companies to hand over technology in exchange for access to the Chinese market.
The last effort at a negotiated solution came in late August with meetings between low-level officials, but nothing came of it. That would basically cover all the imports from China that aren't already covered.
While U.S. businesses in China do not yet appear to face widespread retaliation, some company officials have said they are bracing for blowback.