"We are investigating to find out the cause of the crash," Defence Minister Tea Banh told AFP by telephone.
"Five people were killed and one was seriously injured," he said, adding that the victims were military trainees.
A rescue team and police officers had arrived at the crash site, according to an AFP reporter at the scene who said the wrecked helicopter appeared to be submerged in water in a ditch.
The helicopter was one of 12 choppers Cambodia bought from China last year to boost its military capacity.
In 2008 Cambodia's chief policeman Hok Lundy was killed in a helicopter crash along with the then deputy army commander and two pilots when their chopper went down in bad weather.
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