Two paramedics escaped from their upturned ambulance and rushed to treat a driver trapped in a wrecked car which had smashed into them.

St John Ambulance officers Harrison Smythe and Jared Ranudo were nearing the end of their shift when a Honda crashed into the back of their vehicle on a major Auckland suburban street about 3.30am on Tuesday.

Police said the crash happened after a car was seen speeding on Mt Albert Rd towards Hillsborough Rd.

The impact flipped the ambulance but the shaken paramedics were more concerned about the man who crashed into them and sprang into action to assist.

"We were stopped at the lights at Hillsborough Rd when we heard a loud bang," Ranudo, 27, who was driving the ambulance, said.

"At first I thought our tyres had popped but next thing we spun 180 degrees and we were on our side."

Ranudo ended up sprawled on the floor while Smythe was left hanging in the air by his seat belt and holding on to a door handle.

"Slowly we realised what had happened and that a car had rammed into the back of us," Ranudo said.

"The first thing we did was call for another ambulance and we managed to scramble out the back of our vehicle to see if anyone else was hurt.

"I was shocked and a bit dizzy but Harrison went straight over to the mangled car and it was clear the driver was trapped and in a serious condition.

"Then our training kicked in and we assessed the injured man and Harrison tried to get him out of the car as police arrived at the scene."

Firefighters cut the man from the vehicle and he was taken to Auckland Hospital in a serious condition.

"I suppose I was in a bit of shock but helping the other guy took my mind off my own situation," Smythe, 25, said.

"A second ambulance was called and it took us back to the station where we were checked over but, fortunately, we were both okay."

A few hours later the paramedics were given a round of applause when they attended an early morning leaving do for a colleague at a cafe.

"When we walked in everyone started clapping and our managers praised us for our actions, but we were only doing our jobs," Smythe said.

"We were very lucky and it could have been a lot worse."

The Serious Crash Unit is investigating the incident.