All four were taken to hospital after the incident on State Highway 14 at Maungatapere, Superintendent Matt Srhoj said.
Several police officers were at the scene of an earlier single-car crash, he said, about 8.40pm on Saturday, where the driver of the first car to crash was talking to an officer inside a patrol car.
"A second vehicle has veered across the road and collided with the front of one of the patrol vehicles. Both the police officer and the first driver received minor injuries," Srhoj said.
"Another police officer received moderate injuries after being hit as he attempted to evade the out-of-control vehicles. The driver of the second vehicle also received minor injuries."
Police were investigating what caused the crash and whether charges would be laid, but believed the driver lost control of the vehicle, Srhoj said.
All the officers had been wearing high-visibility gear, and the police vehicles had their flashing lights on, Srhoj said.
All four people taken to hospital had been discharged by late this morning.
"We are extremely grateful that our staff are all going to be okay... We are lucky not to be dealing with a fatality here." Srhoj said.
"They will be sore for a while, but their injuries could have been much worse. We are supporting them and their families while they recover at home."
On New Year's Day, a police officer was killed and another was seriously injured when a car crashed into them in Nelson.
