North Korean leader Kim Jong-un has visited the Chinese Embassy in Pyongyang to express his "deep" condolences over the death of scores of Chinese tourists in a traffic accident in the North, state media said Tuesday.

Kim's rare visit there came amid a thaw in the relations between the communist allies that was highlighted by his surprise trip to China last month ahead of summits with South Korea and the United States.

The North's leader visited the Chinese Embassy at 6:30 a.m. on Monday, the Korean Central News Agency said, as the bus accident occurred Sunday, leaving 32 Chinese tourists dead and two seriously injured. Four North Koreans also died.

"He said that the unexpected accident brought bitter sorrow to his heart and that he couldn't control his grief at the thought of the bereaved families who lost their blood relatives," the KCNA said.

Kim said that North Koreans saw the tragic accident as "their own misfortune" and his country will "take follow-up measures with utmost sincerity" to alleviate the pain of the bereaved families.

It was the first time that North Korea's state media reported a visit by Kim to China's embassy since he took office in late 2011. His late father, Kim Jong-il, often visited the Chinese diplomatic mission, but Kim Jong-un did not do so, reflecting the long strained relations between Pyongyang and Beijing.

Li Jinjun, China's ambassador to North Korea, expressed thanks to the North's leader, stressing his visit to the embassy underscored the two countries' "unbreakable and great friendship," according to the report.

China, North Korea's only remaining ally and economic lifeline, had seen its ties with the North strained due to Pyongyang's nuclear and missile provocations.

But their ties have begun to improve since Kim held a summit with Chinese President Xi Jinping during his visit to Beijing in late March ahead of his planned meetings with South Korean President Moon Jae-in and US President Donald Trump. (Yonhap)