PHNOM PENH, Cambodia — Cambodian Prime Minister Hun Sen said early Tuesday that 339 people died and more than 300 were injured Monday in a stampede on the final day of Cambodia’s annual Water Festival.

That was a drastic boost in the death toll from a statement Sen had made just about an hour beforehand.

The victims were mainly young people who panicked while crossing a bridge during water festival celebrations. The incident happened about 9:30 p.m. local time on Monday.

Emergency service crews have taken the injured to five hospitals around the capital. An unknown number of people jumped off the bridge to avoid the crush, and rescue crews were still looking for them after midnight.

Sen said the government would form a committee to look into the causes of the accident.

Sen said the day should in future be marked as a memorial day, and he sent his condolences to the families of the dead.

Ly Vuthy, a vendor who witnessed the incident, told the German news agency dpa that more than a thousand people were on the bridge trying to leave Diamond Island when one person fainted.

The crowd panicked after an ambulance came to help that person. She said people were packed tightly on the bridge and were unable to move off it.

The water festival is an annual celebration of the end of the monsoon season.

The authorities said last week they expected up to 4 million people to come to Phnom Penh for the festival, more than doubling the capital’s population over the three days.