South Korea's liberal frontrunner for president, Lee Jae-myung, was leading his main conservative rival Kim Moon-soo by more than 10 percentage points in an opinion poll issued on Tuesday, though the race has tightened a week ahead of the election.

Lee, who is the frontrunner in opinion polls for the June 3 election, also said he would "stably manage" relations with China, which he said had reached the "worst state" under the previous administra...