[Updated at 4:25 p.m.] Steve Finch, a Phnom Penh Post reporter, told CNN that the stampede at the water festival in Phnom Penh began around 10 p.m. Monday (10 a.m. ET), when police began firing a water cannon onto a bridge to an island in the center of a river.
The bridge was packed with people, and police fired the water cannon in an effort to get them to move, he said.
"That just caused complete and utter panic," he told CNN in a telephone interview. He said a number of people lost consciousness and fell into the water; some may have died by electric shock, he said.
Watch: "It was chaos," reporter says
Finch cited witnesses as saying that the bridge was festooned with electric lights, which may have played a role in the deaths.
The government denied anyone died by electric shock.
But a doctor who declined to be identified publicly said the main cause of death was suffocation and electric shock. Police were among the dead, he said.
While Finch said the incident apparently coincided with the firing of the water cannon, a witness, Ouk Sokhhoeun, 21, told the Phnom Penh Post that the stampede began first.