"We are investigating a fatality of one of our own members,'' said RCMP spokesman Cpl. Al Fraser.

A female officer was taken to hospital with undetermined injuries. The driver of the semi was treated and released.

The death was another blow to the Alberta RCMP still recovering from the fatal shooting of four officers near Mayerthorpe in March. James Roszko gunned down the Mounties on his farm before taking his own life. They were on the property investigating stolen car parts and a marijuana grow operation.

The officer killed Monday was parked after responding to another traffic accident when his vehicle was struck from behind, said Jules Xavier, a  photographer with the Wetaskiwin Times-Advertiser who witnessed the crash.

"The semi-trailer smacked into the back of the cruiser, forcing it across the north lanes of the QE2, across the median, and across the southbound lanes into the ditch on the southbound side,'' Xavier said.

"By that time the vehicle was just crumpled up like an accordion.''

Xavier said the officer's body was removed from the wreckage and a crew member from an air ambulance unsuccessfully tried to revive him.

The officer was then covered with a blanket, put in a yellow body bag and placed into an ambulance as other RCMP officers hugged each other in grief, he said.

"They pronounced him, then they wrapped him up in a yellow tarp, took all his guns and everything. I knew the guy.''

The name of the dead officer was not released, although police confirmed he was from the Wetaskiwin detachment.

Traffic was rerouted from the Queen Elizabeth Highway near Millet, Alta., onto secondary roads and highways, said Frank Coutney, a County of Wetaskiwin official.

"The highway will be closed until further notice,'' Coutney said.

Queen Elizabeth Highway is the main north-south thoroughfare between Edmonton and Calgary.

Formerly known as Highway 2, it was given the new name by the province to honour the Queen during her recent centennial visit to Alberta.

Millet is about 50 kilometres south of Edmonton.