Two policemen were injured when a car was deliberately driven at them after a routine stop.
One of the officers suffered a fractured skull and bleeding to the brain in the incident in Harpurhey, Manchester, on Sunday night.
A vehicle, believed to be a red Hyundai, was pulled over for speeding in Rochdale Road at about 10.50pm, police said.
When the officers got out to approach the car, the vehicle reversed and hit them before driving off. One of the officers was able to use his radio to call for help and extra patrols were sent to the scene, along with paramedics.
Both were taken to hospital for treatment. One has a fractured wrist, which will need surgery. The other suffered a fractured skull and bleeding to the brain and remains in a stable condition, although his injury is not believed to be life-threatening.
As a result of inquiries by Greater Manchester Police, assisted by Lancashire Police, a warrant was later executed in the Haslingden area of Lancashire where two men were arrested on suspicion of attempted murder. Both remain in police custody for questioning, Greater Manchester Police said. A car has also been recovered for forensic analysis.
Assistant Chief Constable Garry Shewan said: "Sadly, what this incident painfully highlights is the dangers officers face every day when protecting the public. What should have been a routine vehicle stop resulted in two officers being deliberately driven at and suffering serious injuries. I know the friends and colleagues of both officers will be anxious to know how the two men are doing, as it is always very unsettling when friends and colleagues are injured in the line of duty, so we will be offering support to anyone who needs it.
"What I do want to stress is that, as a result of inquiries, we quickly traced what we believe to be the offending car to an address in Haslingden and arrested two people on suspicion of attempted murder. Those individuals remain in custody for questioning and we would continue to appeal to anyone who either witnessed the incident or has information to come forward."
Anyone with information about the incident should call police on 101 or the independent charity Crimestoppers, anonymously, on 0800 555 111.
Ian Hanson, chairman of Greater Manchester Police Federation, said: "This was a wicked and cowardly attack on two decent public servants trying to do nothing more than keep the streets of Greater Manchester safe. What this does is yet again highlight the realities of what policing is in the 21st century. I am sure every colleague and every decent-thinking resident of Greater Manchester wish both officers a swift recovery. Our thoughts are with their family, friends and colleagues."