One woman is dead and three other people are hurt after an ambulance and car collided early Tuesday in Denver.

Denver police say the westbound ambulance had its lights and sirens on when a northbound Cadillac collided with the vehicle in an intersection about 3:20 a.m.

The Cadillac flipped upside down and landed in a residential yard, trapping the driver inside. Firefighters had to cut him out of the car.

A woman was taken to Denver Health Medical Center with critical injuries. She was later pronounced dead.

Police now say it's unclear whether the woman was a pedestrian or a passenger in the Cadillac.

The ambulance was en route to pick up a patient at the time of the crash.