North Korean leader Kim Jong-un has expressed "bitter sorrow" over a bus accident that left 32 Chinese tourists and four North Koreans dead.

The accident took place on Sunday night in North Hwanghae province, when the tour bus plunged off a bridge.

It is rare for North Korea's tightly-controlled media to report on negative news, and for Mr Kim to acknowledge the incident itself is even more unusual.

China is the North's main political ally and largest trading partner.

"[Mr Kim] said that the unexpected accident brought bitter sorrow to his heart," the official KCNA news agency reported.

"He couldn't control his grief at the thought of the bereaved families who lost their blood relatives."

The North Korean leader was pictured visiting injured passengers in hospital. The report said he "personally learned about the treatment".

He also visited the Chinese embassy in Pyongyang, where he met the Chinese ambassador to North Korea Li Jinjun and "expressed his heartfelt condolences and sympathy."