A motorcyclist who died in an accident on the Monaro Highway in Canberra's south has been named as Wayne Morris of Gilmore.

The 59-year-old was killed in the crash involving a truck about 4:50pm (ACDT) on Wednesday near the intersection with Angle Crossing Road.

Officers at the scene described it as one of the most horrific crashes they had encountered.

Traffic Operations Sergeant Rod Anderson said police believed the motorcyclist was travelling south when the collision occurred.

"It appears the motorcyclist died instantly. It's quite a serious and high-speed collision," he said.

Sergeant Anderson said the truck driver was in shock.

"He is in a devastated state and he's receiving support and counselling as we speak," he said.

"He's uninjured but he's badly shaken up by the collision."

The Monaro Highway was closed in both directions for several hours for the crash investigation.

A report is being prepared for the ACT coroner on the accident.

Anyone who witnessed the crash has been urged to contact police.

The family of Mr Morris has requested privacy.

Mr Morris's death is the ninth ACT road fatality this year.