North Korea offers deep apology to China over deadly bus crash

In a message to President Xi Jinping and other Chinese leaders, Kim said the North Korean people were "overcome with sorrow".

"It is, indeed, very sad that the close Chinese friends, who had come here with the feelings of friendship with our people, met with an unexpected accident on our land," the message, carried by the official KCNA news agency, read.

"We make a deep apology to the Chinese comrades for the pain which cannot be alleviated with any word, consolation and compensation," it added.

"Our party and government will make every possible effort to ensure that hours of grief pass and the pains are alleviated even a bit at an early date."

The Chinese tourists and four North Koreans died when a bus crashed off a bridge in North Korea late on Sunday, with two Chinese nationals still in critical condition.

Chinese tourists make up about 80 percent of all foreign visitors to North Korea, says a South Korean think-tank, the Korea Maritime Institute, which estimates that tourism generates revenue of about $44 million each year for the country.

North Korea is a popular, if offbeat, tourist destination for Chinese, especially those from the country's northeast.

China said more than 237,000 Chinese visited in 2012, but stopped publishing the figures in 2013.

China is North Korea's most important economic and diplomatic backer, despite Beijing's anger at Pyongyang's repeated nuclear and missile tests and support for strong United Nations sanctions against North Korea.

However China has welcomed moves by Kim to ease tensions, including his summit this week with South Korean President Moon Jae-in.