An Australian and a Cambodian were killed and a second Australian injured when a landmine was accidentally detonated during a military training exercise west of Phnom Penh, police say.

The Australians were military trainers and another two Cambodian soldiers were also wounded, police in Kampong Speu, 50 kilometres from Phnom Penh, said.

Their names have not yet been released. They said a 45-year old Australian trainer was killed and another 41-year-old Australian was wounded.

Police said the mine detonated at a tank base after the Cambodian who was killed picked up the war-era bomb once it was detected under the ground.

Kampong Speu Provincial Governor Vy Samnang told the Phnom Penh Post it was believed the casualties were shooting at targets around 2pm local time on Thursday when they noticed something on the ground.

“He said they went to pick up the object, a Russian-made bomb, which then exploded,” The Post reported.

Cambodia is littered with unexploded ordnance (UXOs), a legacy of three decades of civil war. However, casualty figures have steadily come down over the past two decades thanks to an international effort to rid the country of the blight.

Kampong Speu Provincial Hospital health department director O Vann Then said the three injured people had received “light injuries” to their hands.

“The body of the Cambodian soldier has already been taken out by family while the Australian body is still at the hospital waiting to be taken by the Australian embassy,” Mr Then said.

The injured are being treated at Kampong Speu hospital, east of Phnom Penh.

Some 60,000 Cambodians have been killed or wounded by mines since they were first deployed in large numbers in 1979, when the genocidal Khmer Rouge regime was ousted from power and began 18 years of guerrilla warfare.

Prime Minister Hun Sen said last year that land mines continue to kill or maim nearly 100 people per year, and the country needs more than $400 million in aid to remove all of them by 2025.

Cambodia has cleared about 1500 square kilometres of mines, but nearly 2000 square kilometres of land remains littered with the munitions, Mr Sen said.

The Australian embassy in Phnom Penh declined to comment while a Cambodian government spokesman was unavailable for comment.

-with ABC