In the past eight days more than 14 cars have been set alight in the Christchurch area.
Last night four cars were set alight within an hour and police believe the fires are linked, with footage being shown on social networking internet sites.
The first fire happened at10.25pm in Lyttelton. That was followed by fires at 10.53pm at Mt Pleasant, 11.09pm in Edgeware and 11.19pm in Avondale.
Detective Senior Sergeant Wormald said there is no pattern to the type of car being targeted.
"The only thing that's consistent is that they are parked on the side of the road," he said.
Given the nature of the fires and the serious risk they pose to the public and emergency services, police said their investigations have been intensified.
Mr Wormald said footage of the fires or comments about them could be appearing on social networking sites like Bebo.
"It's possible that people are posting information in chatrooms about what they are doing and what others are doing," Mr Wormald said.
Investigations have so far confirmed at least two people are involved as witnesses saw them and their vehicle leaving the scene of one of last weeks' fires.
Police urge anyone with any information to contact Christchurch central police station 03 363740 as the car fires could potentially cause major damage to property and people.
