The alarm came to the police at 00.28 during the night towards Friday.
Witnesses had then seen how a man walked around and lit things around Fridhemsplan.
- There has been talk of two bicycles burning on a pile of boards lying on the ground, says Pontus Sandulf, officer on duty at the police.
The fires must have started in different places around the same intersection.
The police and rescue service were on site after only two minutes and the man was arrested in the act.
The fire was extinguished without any major drama. The man is now suspected of aggravated arson as the fire could have spread if it had not been discovered in time. It is unclear why he did as he did.