"Uncertainties are increasing in the international and regional situation," state broadcaster CCTV reported Xi as telling Lee in a congratulatory message.

"I attach great importance to the development of China-South Korea relations," he said.

Lee won a snap election triggered by his predecessor's disastrous martial law declaration in December.

Lee scored a thumping victory over conservative Kim Moon-soo of disgraced ex-president Yoon Suk Yeol's former party in the snap poll, with Lee's term beginning immediately after the vote tally was certified early Wednesday.

CCTV said Xi told Lee that China "is willing to work with the South Korean side to uphold the original intention of establishing diplomatic relations" and "good-neighbourly friendship".