China could stop buying coal from North Korea to punish the ally for its recent nuclear test, a South Korean expert suggested Thursday amid calls for Beijing to take a firmer stance against Pyongyang.

China has come under growing pressure from South Korea and the United States to help draw a strong sanctions resolution from the U.N. Security Council to punish the North for its fourth nuclear test last week.

Choi Kyung-soo, president of the North Korea Resources Institute in Seoul, noted the North's high reliance on trade with China.

"Coal exports account for nearly half of all North Korean exports to China," he said in a phone interview with Yonhap News Agency. North Korea earned $2.84 billion from exports to China in 2014, nearly 90 percent of the $3.16 billion earned in total, according to data from the institute and the Korea Trade-Investment Promotion Agency.

Coal made up some 40 percent of exports to China at $1.14 billion.

If China boycotts North Korean coal, the North's leader Kim Jong-un will likely have trouble raising the funds necessary to run the country and build its nuclear and missile arsenal, Choi said.

Without Chinese demand, North Korea's mining industry could also suffer, leading to the collapse of a major sector supporting the country's economy. This could fuel public unrest with many miners not being paid wages.

"It won't be easy for the Chinese government to decide to stop coal imports because it will have to find a substitute to prevent causing a disruption to the production of Chinese firms," Choi said.

Still, China could cite its economic stagnation and stricter international environmental standards to ban or limit North Korean coal imports, he said.

Despite China's stated goal of denuclearization of the Korean Peninsula, many analysts are skeptical that it will strengthen sanctions on the North because it wants to keep Pyongyang as a buffer against American troops in U.S.-backed South Korea. (Yonhap)