The comments from China's commerce ministry came days after the highest US court dealt President Donald Trump a stinging defeat by striking down many of the tariffs he has used in a global trade war, including some against rival China.
Within hours of the ruling, Trump said he would impose a new 10 per cent duty on US imports from all countries starting on Tuesday, only then to lift it to 15 per cent in a move that seemed to surprise some of his own officials.
"US unilateral tariffs ... violate international trade rules and US domestic law, and are not in the interests of any party," the Chinese ministry said on Monday.
"Co-operation between China and the United States is beneficial to both sides, but fighting is harmful."
Trade and tariffs are expected to dominate the agenda for both China and the US before a visit by Trump to China in late March and early April, when he will meet his Chinese counterpart, Xi Jinping.
Trump's planned new levies are grounded in a separate but untested law, known as Section 122, that allows tariffs up to 15 per cent but requires congressional approval to extend them after 150 days.
No president has previously invoked Section 122, and its use could lead to further legal challenges.
"China will continue to pay close attention to this and firmly safeguard its interests," the commerce ministry said.
The US court's ruling invalidated a number of tariffs that the Trump administration had imposed on Asian export powerhouses from China and South Korea to Japan and Taiwan, the world's largest chipmaker and a key player in tech supply chains.
South Korea said it would continue to consult with the US to maintain a "balance of interests" between the two countries, while its industry minister said there was concern among officals across industries, including cars, batteries and chips.
"The public and private sector need to work together to secure Korean companies' export competitiveness and diversify their markets," Industry Minister Kim Jung-kwan said on Monday.
India said it had delayed plans to send a trade delegation to Washington this week to finalise an interim trade deal, chiefly because of fresh tariff uncertainty out of the US.
