An on-duty police officer and a 91-year-old woman have died following a crash on the A4 in Berkshire.
PC James Dixon died after the motorcycle he was riding was in collision with a car on Bath Road near Hare Hatch at 13:50 GMT.
The pensioner, who was a passenger in the car, was killed while the driver, also a woman, was taken to hospital.
Officers said the road would remain closed for the remainder of Tuesday.
Thames Valley Police said the next of kin of both PC Dixon and the deceased woman have been informed.
A force spokesman said officers remained at the scene of the collision and had advised motorists to avoid the area.
Investigators at scene
The incident has been referred to the Independent Police Complaints Commission (IPCC).
IPCC Associate Commissioner Guido Liguori said: “My thoughts and sympathies are with their families and friends and the colleagues of the officer at this very difficult time.
“IPCC investigators are attending the scene as part of an independent investigation to determine the circumstances which lead to the collision.”
PC Dixon was based at Loddon Valley police station, near Reading.
Police said the injuries of the driver involved are “not thought to be life threatening”.
Tributes to PC Dixon have been posted in comments on Thames Valley Police’s Facebook page.
Daniel Ruffle said: “Ride the sky and the clouds big man, it was a pleasure knowing you and working with you.”
Bernadette Ellison said: “God bless you Dixie, you made me laugh with your wicked sense of humour.”