Police and fire crews responded to fires in several areas of Gothenburg as well as nearby Trollhättan, Lysekil and Falkenberg.
The night of unrest where masked youths were also seen throwing stones at the police also touched parts of Stockholm and Uppsala with a reported 10 cars set on fire.
"We realised that it can't be a coincidence that it started in such a short period of time in several places," said Ulla Brehm, spokesperson for police in western Sweden." We have our colleague in intelligence working on this and checking the internet, so yes, it is a theory we are working on."
Police later arrested two arson suspects in Frölunda aged between 16 and 21 who they say are criminals and known to them.
Ulla Brehm told Radio Sweden that they had a lot of witnesses helping them identify suspects.
"We have made several identifications on the spot and early morning we started something that we do with yongsters under 18, we visit the parents. We say to them we want to talk about your child and what is going on," spokesperson Ulla Brehm told Radio Sweden.
In recent years, youths have set fire to cars a week or so before the start of school.
Law and order is one of the issues in the upcoming general election. Prime minister Stefan Löfven of the Social Democrats was interviewed by Swedish Radio this morning as part of a series of party leader interviews in the next fortnight. He said he was "really getting mad" by the criminal attacks on property and said that society "will react strongly".