South Korea's Lee says he asked Xi to play a mediating role on North Korea

South Korean President Lee Jae Myung said on Wednesday that much progress had been made in restoring trust with Beijing, and that he had asked Chinese President Xi Jinping to play a role in mediating Seoul's efforts to engage North Korea.

Lee, who held talks with Xi this week, said the Chinese leader had noted patience was needed when they discussed nuclear-armed North Korea. Lee was speaking to South Korean media in Shanghai with his remarks relayed live on television.

The South Korean president said he laid out the efforts - so far without success - that Seoul had been making to engage North Korea in dialogue and improve relations, and asked Xi to play a role to mediate for peace on the Korean peninsula.

"President Xi acknowledged our efforts so far and said patience is needed," Lee said.

Lee has been on a state visit to China and his meeting with Xi was their second in less than three months.

Lee has sought to open a "new phase" in ties with China, after several frosty years and with South Korea's popular cultural exports being shut out of the Chinese market due to a dispute over a US missile defence system deployment in South Korea in 2017.

"President Xi said 'talk is easy, but action is not so easy,'" Lee said, as he talked about how building trust and respect between countries takes work.

Diplomatic relations are inherently complex in balancing each other's key national interests, Lee said he had told Xi, adding he hoped recent tension between Tokyo and Beijing could be resolved.

Lee said South Korea considered its ties with Japan as important as its relations with China.