At least 339 people have been killed in a stampede during festival celebrations in the Cambodian capital, Phnom Penh, Prime Minister Hun Sen has said.

Huge crowds had gathered on a small island for the Water Festival, one of the main events in the Cambodian year.

The stampede took place on a bridge. An eyewitness told AP news agency the trouble began when 10 people fell unconscious in the crowd.

The BBC's Mike Wooldridge says it is a "tragedy on a rapidly growing scale".