A doorman at a Beijing kindergarten has stabbed 15 children, killing one of them, according to Chinese state media.

Three teachers were also injured when the knife-wielding man went on the rampage at a nursery in Beijing University's Number One Hospital.

The alleged attacker, 51-year-old Xu Heping, has now been detained by police for questioning.

The motive for the stabbing is unclear, but Mr Xu is said to have had a history of mental illness. The incident was "the worst attack on children in the capital in decades", according to China Central Television (CCTV).

Early on Wednesday morning, police received an emergency call saying that a man had been "hacking people up at the kindergarten" with a kitchen knife, according to the website sina.com.

Eight officers went to the scene, where they soon overpowered and arrested the man, the website said.

A four-year-old boy died due to serious injuries and blood loss.

Two other children and a teacher sustained serious neck wounds, and are in a critical condition, according to Xinhua news agency.

The other victims were said to be "covered in blood", but their injuries were not thought to be life-threatening.

"It was too cruel, it happened in a moment or so. The victims were just kids and I saw the bodies dangling inside the emergency cars," one woman told CCTV. Another witness told the Associated Press news agency: "Blood was everywhere. The kids were lying on the ground."