A police officer and a 61-year-old woman died in a crash on Christmas Day.
The 46-year-old officer was responding to an incident when the marked BMW 3 Series he was driving was in collision with a Citroen C3 on the A57 in Sheffield.
South Yorkshire Police said the officer died at the scene and the woman, who was a passenger in the second vehicle, died in hospital.
The collision happened near to Coisley Hill at about 20:15 GMT.
A force spokesman said the officer was responding to an "immediate incident" when he was in collision with the silver Citroen which was travelling in the opposite direction.
The woman who died was from Sheffield, he added.
A 63-year-old man who was driving the Citroen was taken to hospital where he remains in a serious condition.
Assistant Chief Constable of South Yorkshire David Hartley, said: "On behalf of the force I'd like to offer my sincere condolences to all of those left bereaved by this terrible tragedy - our thoughts, love and support are extended to all those affected.
"We are doing everything we can to support them through this difficult time."
He went on to pay tribute to the officer killed in the collision.
"We have lost a friend and a colleague from our police family in this incident," ACC Hartley added.
"The officer has been with us for 12 years and was a passionate, professional and universally liked officer.
"His colleagues, and everyone across the force, are devastated by what has happened."
The force said the collision had been referred to the Independent Police Complaints Commission.