Red, white and blue cars were set alight on different streets over a four-hour period in Upper Hutt last night.
Police detectives are investigating the suspected arsons this morning with the assistance of fire safety officers.
The first fire was a red Honda Civic, which was set alight on McLeod St, Elderslea about 1.45am.
The second was in Gillespies Rd, Birchville where a blue Nissan Sentra was lit about 4.40am.
The final fire was at 6.10am where a white Mazda Demio was set alight in Alleyne Ct, Brown Owl.
Senior Sergeant Marc Clausen said all the cars were significantly damaged.
Anyone who saw people acting suspiciously in any of those areas overnight should call Hutt Valley CIB on 04 560 2600 or Crime Stoppers on 0800 555 111.