China's ambassador to the US, Cui Tiankai, said the potential spread of nuclear weapons would not bring security to the highly-tensed region.
"It could only make things much worse. We are certainly opposed to the existence of nuclear weapons anywhere on the Korean peninsula or anywhere," the Hong Kong-based South China Morning Post quoted Cui as having told reporters in Washington on Friday.
The comments came on a day North Korea launched its second intermediate-range missile over the Japanese territory in less than a month. The missile test was the first after Pyongyang tested its sixth and largest nuclear device on September 3.
The North Korean state media said the reclusive nation's aim was to seek an "equilibrium" of military force with the US after an emergency meeting of the UN Security Council again condemned the Pyongyang's nuclear and missile tests.
Ambassador Cui said China understood South Korea's fears.
"We are willing to help them to solve these concerns on the condition of not risking China's security interests," he said, apparently referring to US deployment of the Terminal High Altitude Area Defence (THAAD) weapons in South Korea.
The deployment of nuclear weapons in South Korea and Japan will bring them to the doorstep of China.