Man threatens police, steals patrol car

South Australian police have arrested a man, after he allegedly threatened police with a knife, and then stole a patrol car.

Police say the 21-year-old from Magill, crashed into a pole on Osmond Tce at Norwood, in Adelaide's eastern suburbs at about 12.30pm.

He then drove off, but was found a short time later by police in Vernon St nearby.

"A police patrol attended and found a red Nissan coupe in Vernon St Norwood and started speaking with the driver," Acting Chief Inspector, Stephen Howard said.

"Another patrol in an unmarked police car backed up and also attended Vernon St,"

"While the three police officers were talking with the driver of the red Nissan, he became agitated and pulled a knife on the officers."

When the knife was pulled out, Police began to back away from the man, and he jumped into the unmarked patrol car.

A policeman was able to release pepper spray inside the car, at the man, as he allegedly drove at the police officers and then drove off.

"And in that process, collided with a number of parked vehicles,"

"Six vehicles were damaged in total, including the marked police car," Acting Chief Insp Howard said.

Police arrested the man and he was taken to the Royal Adelaide Hospital for a medical assessment.

Police say one he is released, he is expected to be taken to the City Watch House to face charges.