By Agence France-Presse
Washington imposed levies on $16 billion of imports, sparking an immediate retaliation in kind from Beijing, which said it "firmly opposes the tariffs and has no choice but to continue to make the necessary counter-attacks".
It also said the US was "clearly suspected" of violating World Trade Organization rules and would file a lawsuit with the group.
The measures are the second after the world's top two economies swapped tariffs on $34 billion of goods in July.
They come as officials from each side hold their first talks since June aimed at easing a row that has dragged on equities for months. However, observers are cautious about what progress they will make initially.
Most stock markets were down in Asia.
While Tokyo edged up 0.2 percent in the afternoon, at the break Hong Kong was 0.7 percent down and Shanghai lost 0.3 percent. Seoul slipped 0.1 percent but Singapore surged 1.5 percent, after a one-day holiday.
Sydney fell 0.2 percent -- and the local dollar shed 0.8 percent -- as Australia's Prime Minister Malcolm Turnbull fights for his political life following a leadership challenge.
The S&P/ASX 200 was also being dragged by a near five percent plunge in Qantas as a jump in the airline's profits was offset by its worries about rising fuel costs.
Dollar picks up
Investors are keeping tabs on developments in Washington after Trump's former personal adviser admitted a series of charges including illegal use of election funds, while his ex-campaign manager was convicted on several counts including bank and tax fraud.
On currency markets the dollar sprang back to life against the yen, pound and euro after this week's travails, with Federal Reserve minutes signalling it is ready to lift rates again as the economy continues to improve.
"Many participants suggested that if incoming data continued to support their current economic outlook, it would likely soon be appropriate to take another step," the minutes said.
The greenback had taken a hit this week from Donald Trump's comments criticising the central bank's rate increases and accusing it of not backing his economic plan.
However, the Fed's policy committee pointed to "ongoing trade disagreements and proposed trade measures as an important source of uncertainty and risks".
In addition, most members said "an escalation in international trade disputes was a potentially consequential downside risk for real activity".
Attention now turns to this week's annual central bankers' symposium at Jackson Hole in Wyoming, with investors hoping for some idea about governors' plans in light of the China-US trade row.
Key figures around 0500 GMT
Tokyo - Nikkei 225: UP 0.2 percent at 22,406.98
Hong Kong - Hang Seng: DOWN 0.7 percent at 27,727.06 (break)
Shanghai - Composite: DOWN 0.3 percent at 2,705.40 (break)
Euro/dollar: DOWN at $1.1554 from $1.1595 at 2100 GMT
Pound/dollar: DOWN at $1.2867 from $1.2914
Dollar/yen: UP at 110.82 yen from 110.60 yen
Oil - West Texas Intermediate: UP two cents at $67.88 per barrel
Oil - Brent Crude: DOWN 16 cents at $74.62 per barrel
New York - Dow Jones: DOWN 0.3 percent at 25,733.60 (close)
London - FTSE 100: UP 0.1 percent at 7,574.24 (close)