The United States and China have imposed a fresh round of tariffs on an additional $16bn (£12bn) of each other's goods.
The 25% levies took effect as officials from the economic superpowers met for talks in Washington over the escalating trade war.
They follow last month's first round of tariff increases of the same size by both sides on $34bn (£26bn) of each other's imports – taking the total to $50bn (£39bn).
The US was the first to impose the latest round of tariffs on goods including plastics and chemicals, which China vowed to "counter-attack" with levies on products such as steel, coal and medical equipment.
Beijing criticised the US increase as a violation of World Trade Organisation rules and said it would file a new complaint to the body.
US president Donald Trump has threatened to target all $500bn of Chinese imports unless Beijing agrees to sweeping changes to its intellectual property practices over what his administration alleges are unfair trade practices.
China denies the allegations and its state media has said Beijing will not be cowed by Washington's threats.
China exported goods worth $505.5bn to the US in 2007, compared with $129.9bn of American goods sent to China.
Mr Trump has also increased tariffs on imports from the EU and other countries including Canada and Mexico as he pushes ahead with his campaign pledge to protect American jobs. He has described trading relationships with his neighbours and allies as unfair.
The trade war risks significantly raising prices for consumers, while global stock markets, which have largely ignored Mr Trump's complaints as "bluster" and a negotiating ploy, are getting more jittery as nations retaliate.
The International Monetary Fund has warned the escalating trade dispute threatens to derail the global economic recovery and growth.
Mr Trump's tariffs and retaliation by trading partners could cut global economic output by 0.5% from projections for 2020.
That translates to almost $500bn in lost annual output.
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"The risk that current trade tensions escalate further with adverse effects on confidence, asset prices and investment is the greatest near-term risk to global growth," IMF chief economist Maury Obstfeld told a news conference last month.
Still pending is the possibility of new duties on an additional $200bn worth of Chinese imports, which are the subject of public hearings in Washington this week.