Police were alerted to the first of the fires just before midnight, when a blaze was reported at the Kampen School, reports broadcaster NRK.
When responders arrived at the scene two cars were also alight, according to the report.
“We've had three incidences of fire in a relatively short period in the Grønland-Kampen area,” operation leader Steinar Hausvik told NRK.
“There were also cars that caught fire. Nobody has been arrested in connection with [the fires]. We presume the fires were started deliberately,” Hausvik added.
A second fire was reported to police, this time located in a back yard, 30-40 minutes after the initial report.
Cardboard stored against a wall had caught ablaze in the second fire, writes NRK.
Police told the broadcaster they also believed that fire to have been set deliberately.
A fire in a container in the Grønland neighbourhood shortly afterwards became the third in the area to which emergency services responded on Tuesday night.
“It is not possible to say with certainty that there is a connection [between the fires], but it is reasonable to suggest that there is a connection. [The fires] could have been started by the same persons, but we do not have evidence for that at this stage, though we do have a theory,” Hausvik told NRK.
Police currently have no descriptions of individuals suspected of starting the fires. One potential suspect may have been wearing a reflective patch or strip on his or her back, according to the report.
Police are collecting witness statements on an ongoing basis, writes NRK.
All three fires have now been extinguished.