South Korea temporarily tightened restrictions on entry to its territory for Chinese residents on Saturday, on the eve of a meeting with US President Donald Trump and US Secretary of State Rex Tillerson.
The government said it was acting to protect South Koreans and foreigners against acts that violate human rights and other considerations, the official Yonhap news agency said.
More than 28,000 US troops are stationed in South Korea to deter potential aggression from the North Korean regime.
The South Korean presidency has been unwilling to deploy missiles capable of delivering nuclear warheads close to the Chinese border as a concession, but has promised sanctions and added pressure on North Korea.
Beijing has already voiced its concerns to Seoul, saying the measures could harm trade.
South Korea, which has introduced a retail sales tax, has raised taxes on film tickets and credit cards to finance the two countries’ military deployments.
In 2017, the two countries’ economic relationship totalled $220bn, dwarfing trade with other third-party countries such as Japan and the European Union.
Last week, China’s foreign ministry summoned a South Korean ambassador in Beijing to protest at the decision to cancel a naval drill following North Korea’s February nuclear test.