About five North Korean restaurants in China's northeastern border towns have closed their doors for unknown reasons, a source with knowledge of the matter said Tuesday, amid speculation that Chinese authorities might have refused to renew visas for North Korean waitresses working there.

The shutdown of the North Korean restaurants in China's border cities of Yanji and Hunchun took place after the U.N. Security Council adopted new sanctions against North Korea's nuclear and missile programs.

"Among the North Korean restaurants in Yanji and Hunchun, some of which sell drinks and offer performances, (some) were shut down and their serving staff have disappeared," the source in the Yanbian Korean Autonomous Prefecture of China said on the condition of anonymity.

It was not clear why the North Korean restaurants were shut down, but the source said Chinese local government officials "were already aware of the situation."

There has been speculation that Chinese authorities might have refused to renew visas for the North Korean waitresses, according to the source.

China has vowed to earnestly implement the new U.N. sanctions against North Korea's nuclear and missile programs, but made it clear that sanctions should not affect normal trade between Pyongyang and Beijing.

Many analysts believe that China won't put crippling economic pressure on North Korea due to fears over a collapse of the North Korean economy.

South Korea has urged its citizens living in or traveling to China to avoid eating at North Korean restaurants as part of its efforts to cut off any cash flow to North Korea.

North Korea is estimated to operate about 100 restaurants in China, a legitimate revenue source for the cash-strapped country. (Yonhap)