An Auckland police officer suffered gashes to his arm and face after being assaulted by a man in Flat Bush in a violent and unprovoked attack.

A witness said the officer pulled over a vehicle on Haddington Drive in Flat Bush about midday yesterday.

"The officer pulls over the young man, man gets out of car, runs up to officer and starts to punch and officer gets thrown to ground and his glasses smash in his eyes," the witness said.

After being alerted to the attack, emergency services, including nearly a dozen police cars and ambulance, rushed to the scene.

Inspector Wendy Spiller, Area Commander for Counties Manukau East, said the alleged offender immediately began punching the officer in the head a number of times and an altercation took place between them.

"The officer was taken to an A&E where he was checked over. He has a broken finger and a number of bruises, thankfully he has not suffered any serious head injury. He is being well supported by his colleagues and the wider organisation."

A 25-year-old man has been charged with assaults with intent to injure, operating a motor vehicle recklessly and failing to stop. He is due to appear in Manukau District Court tomorrow.

"It is completely unacceptable that any person would assault a police officer, completely unprovoked when they are simply doing their job," Spiller said.

"They leave their families every day to serve our communities and they deserve to go home safely."

The witness said it looked like the man saw the officer waiting at the intersection and slammed his brakes on and parked his car.

"The cop turned his lights on and pulled behind him. No words were spoken, the man just got out and sprinted up to the officer, instantly attacking him," the witness said.

She said the officer was holding his face, talking about his eyes.

"His glasses smashed on the road during the incident and it looked like they may have smashed into his eyes," she said.

"He had lumps on his forehead and gashes on his shoulder and arms."

The witness told the Herald the officer was taken to the emergency department and the attacker was arrested and taken into custody.

She described the officer trying to defend himself and a member of the public stepping in to hold the attacker, while the police officer called for backup.

"Within 30 seconds, 10 cop cars arrived," she said.