China from Wednesday required travelers arriving from South Korea to present a COVID-19 test.
Many see this as a tit-for-tat move by Beijing in response to Seoul's similar demand from travelers arriving from China.
A notice was sent to airlines operating between the two countries on Tuesday, Seoul-based Yonhap reported, citing unnamed officials as saying "Chinese aviation authorities said all passengers on board direct flights from South Korea to China will receive polymerase chain reaction (PCR) tests on arrival."
"Those who test positive are required to be quarantined or hospitalized," it added.
Seoul has imposed similar restrictions on travelers from China after the world's most populated nation fully reopened last month amid a spike in COVID-19 cases.
Such tests are not required for other international visitors entering China.
Mao Ning, a Chinese Foreign Ministry spokeswoman, said at a news conference in Beijing on Tuesday that "Regrettably, a handful of countries have insisted on imposing discriminatory entry restrictions targeting China. China firmly rejects this and has reason to take reciprocal measures as necessary."
Calling an end to what Beijing calls the "politicization of COVID-19 measures," Mao said such "discriminatory restrictions targeting China should be removed."
"We are ready to work with all countries to better facilitate normal cross-border travel," she added.
On the other hand, a South Korean Foreign Ministry official said: "China should not restrict people's entry across its border for reasons other than those of pandemic response measures."
After Seoul's anti-virus measures against travelers coming from China, Beijing had suspended its free transit policy with South Korea and had also halted granting short-term visas to South Koreans.
