South Korea would have to side with the United States if the ally collides with China over the disputed South China Sea, an expert in Asia-Pacific affairs said Thursday.

"In case of an emergency in the South China Sea, South Korea would have no choice but to move in accordance of the South Korea-U.S. alliance," Shin Gi-wook, a professor at Stanford University in California, said in a lecture hosted by the Korea Institute for Defense Analyses.

South Korea appears to be under growing dilemma as the two superpowers ratcheted up tension over China's claims of the area, also claimed by Vietnam and the Philippines.

Last month, the U.S. sailed the Lassen warship close to China's artificial islands in the South China Sea, prompting fears of a possible military conflict.

The U.S.-China tension has sparked a security question on which side the South would take if the countries had an armed clash.

"Flexibility is necessary, but what's more important is a principle," Shin said, advising Seoul to prioritize the South Korea-U.S. alliance over the strategic partnership between Seoul and Beijing.

Still, the superpowers may be free from a potential clash in the South China Sea because "despite China's eagerness to show off its power, the country is practically incapable yet."

South Korea tends to think the power of China is growing equal to that of the U.S. as the country tries to reposition itself between the two superpowers and pitch itself as a balancer, Shin said.

"But the 'balancer' discourse could cause unnecessary misunderstanding," the professor said, adding, "South Korea needs to make it more clear that the central axis of South Korea's security and diplomacy is the South Korea-U.S. alliance.

"China does not have the willingness and the power to replace the U.S. (as the controller of the global system)," he said. "South Korea should not be deluded by China's recent charm offensive."

Under this backdrop, Seoul could play its role as a defuser whenever U.S.-China tensions escalate, Shin said, adding that leading the efforts to denuclearize North Korea could be part of the role. (Yonhap)