China on Sunday declined to be drawn on the prospect of a summit between President Xi Jinping and nuclear-armed North Korea's Kim Jong-Un, who is slated to visit Moscow later this year in his first trip as leader.

Beijing is Pyongyang's main ally, diplomatic protector and economic buttress, their ties forged in the blood of the Korean War, but Kim has yet to visit three years after coming to power following the death of his father Kim Jong-Il.

In contrast Xi has met South Korean President Park Geun-Hye several times, while China's patience has been tried by the North's antics.

The Chinese leader's first visit as head of state to the Korean peninsula last year was to the capitalist South rather than the North.

Moscow said in January that Kim would be among those attending ceremonies to mark the 70th anniversary of the Soviet Union's victory over Nazi Germany in World War II.

Such a move would reflect warming relations between Pyongyang and Moscow, and signal a desire on Kim's part to reduce his country's dependence on China.

Asked whether Xi and Kim would meet this year, Chinese Foreign Minister Wang Yi said: "When our leaders will meet will have to suit the schedules of both sides."

"China and the DPRK are friendly neighbours," he told a press conference on the sidelines of the National People's Congress, China's communist-controlled parliament, using the abbreviation for the North's official name, the Democratic People's Republic of Korea.

"We cherish our traditional friendship with the DPRK and we seek the normal development of our relations," he added.

Beijing and Seoul are growing closer in fields ranging from business and tourism to history and diplomacy, sharing a critical stance over Japan's 20th-century invasion and occupation of both countries.

Wang reiterated China's regular exhortations for calm and stability on the Korean peninsula.