In 90 minutes, about 15 alarms came about fires in Eskilstuna during the night towards Monday.
It is suspected to be revenge for the police arresting a leader in the criminal networks in the city.
The rescue service had to travel by shuttle traffic and did not have time to respond to all alarms - and the concern is now growing in the city that the fires will continue.
- I understand that they are worried, I am too, says Christer Sjöqvist, police area chief in Eskilstuna.
Both the police and the rescue service are now preparing to cope with new attacks on Tuesday night.
The rescue service has brought in personnel from, among others, Västerås and Strängnäs.
And it has been called to a meeting during the evening where the police and rescue services will prepare for how to deal with new violence.
See Oskar Jönsson's report from Eskilstuna in the clip above.