Police and the fire service are investigating the cause of the fires, and are keeping an open mind on whether they are all linked.
The first fire started when somebody put a cardboard box under a car parked in a driveway and set it alight about 11.35pm on Thursday.
The blaze caused damage to the rear of the vehicle before being put out.
About 20 minutes later, a fire was lit in vegetation near a reservoir, and at 12.20am on Friday a number of large palm trees were set alight.
Whangarei police Detective Constable Wayne Pirret said the latter two fires were started by the same method and he was concerned there was an arsonist at work.
"We can't say for sure at this stage if they are all linked, but we are keeping an open mind on whether they were [caused by] the same people," Mr Pirret said.
"But we are concerned that there could be a firebug, or bugs, out there and if they don't stop we could have serious harm caused to people or significant property damage." He said arson was a serious offence, punishable by up to 14 years' jail, while if a death or injury occurred charges that had even longer jail terms would be laid.
Mr Pirret said the public had a part to play in helping catch the firebug and he urged anybody with any information, or who may have seen any suspicious people or vehicles in the areas around the times of the fires, to ring the Crimestoppers.
Mr Bain said that, while the deliberate fires were all nuisance blazes, if left unattended they could quickly turn into something far more serious and become a threat to life or property.
He said anybody who saw anybody acting suspiciously in the area should ring 111.
