A police officer was thrown under his vehicle and knocked unconscious while helping a broken-down driver.
A sergeant and police constable attended the A361 at Landkey, North Devon, at about 17:42 GMT on Friday.
The pair were hit when a Citroen C4 crashed into the back of their vehicle, causing one of the officers to become trapped.
Ch Supt Matt Lawler said he was "relieved" the officers "were not more seriously injured".
They had been assisting a broken-down driver at the roadside for about 15 minutes when their vehicle was struck by a 77-year-old female driver from Bideford.
The force of the crash propelled the sergeant into the verge and the police constable beneath his vehicle.
The pair were stood at the nearside of the road in line with their training when they were hit, Devon and Cornwall Police said.
The Citreon rebounded into the opposite carriageway, colliding with another vehicle which subsequently hit a further motorist.
The sergeant, who suffered minor injuries, was able to remove his colleague from under the police vehicle, where he was taken to North Devon District Hospital for assessment.
Ch Supt Matt Lawler said: "This was a truly frightening experience for everyone involved, especially for the officer who regained consciousness whilst still lying underneath his own police vehicle, and I pay tribute to the courage and focus of his sergeant in coming to his aid."
Both officers are recovering at home while being supported by their families, police said.
The driver of the Citreon C4 was uninjured, but was also taken to hospital for observations.
Police confirmed the driver of the broken-down vehicle was arrested at the scene on suspicion of driving under the influence of drugs.