Foreign Minister Wang Yi cautiously welcomed Seoul's announcement that Pyongyang had offered to hold denuclearisation talks with the United States in return for security guarantees.

The North also agreed to hold a historic summit between its leader Kim Jong Un and South Korean President Moon Jae-in in late April.

"The Korean peninsula issue has finally taken an important step in the right direction," Wang told a press conference on the sidelines of annual parliamentary session.

"These initial steps must be followed up by corresponding and concerted efforts by the parties. We call on the parties, particularly the United States and the DPRK, to engage in dialogue sooner rather than later," he said.

But Wang issued a word of caution, noting that breakthroughs on the North Korean nuclear issue had collapsed in the past.

"Of course it takes more than one cold day to freeze three feet of ice," he said.

"Despite light at the end of the tunnel, the journey ahead won't be smooth. History has reminded us time and again that whenever tensions subsided on the peninsula the situation would be clouded by various interferences," he said.

"Now is the crucial moment to test the sincerity of the parties to solve the nuclear issue."

Wang's comments come as two South Korean envoys left for Washington to brief US officials on the North's offer, after their landmark visit to meet Kim in Pyongyang.

According to Seoul, Kim said the North wanted to talk to the US and would not need nuclear weapons if the country's security was guaranteed.

Envoy Chung Eui-yong, head of Seoul's National Security Office, will travel to China and Russia following his Washington trip.

- Breakthrough or ploy? -

Wang said the security concerns of North Korea must be addressed in return for progress towards denuclearisation.

Under pressure from US President Donald Trump, Beijing has backed a series of United Nations sanctions against North Korea, sending relations between the Cold War-era allies to a new low.

Beijing has repeatedly called for negotiations to peacefully put an end to tensions that have raised fears of nuclear warfare, after months of fiery rhetoric between Kim and Trump.

Wang said China's proposal for the United States, Japan and South Korea to suspend joint military drills in the region in return for North Korea halting its nuclear and missile tests was "the right prescription".

In Tokyo, which has seen North Korea test ballistic missiles over its airspace, Japanese Prime Minister Shinzo Abe warned that North Korea's offer of denuclearisation talks with Washington could be a ploy to play for time.

"I've repeatedly said that we have to create a situation of putting maximum pressure on North Korea so that the North wants to have talks with us," Abe told MPs.

"However... it is true that the North has in the past earned time to develop nuclear capabilities and missiles" during periods of negotiation, Abe cautioned.

"Talks for the sake of talks are meaningless and we should never loosen sanctions just because North Korea is open to talks."