Road policing Inspector Wayne Ewers said Northland police had Auckland colleagues told them a stolen car was northbound.
Police spotted the vehicle just south of Whangarei but the driver would not stop, and headed to Whangarei, driving through Morningside and onto Porowini Ave.
Ewers said heavy traffic impeded the girls' escape. The car continued along Porowini Ave but collided with the police car.
The police car's airbags inflated but the driver was not injured. However, it is thought the police car, estimated to be worth $50,000, will be written off.
The six teenagers were arrested quickly.
"It was lucky no one else was involved given the heavy traffic at the time," Ewers said.
He said it was likely the girls' cases would be dealt with in Auckland.