During the day, hundreds of young people rode mopeds through Stockholm. They then gathered in Frihamnen.
There have been major traffic disruptions, says Sylvia Oldin, the police duty officer, to TT.
When the police arrived at Frihamnen, several young people began throwing stones at the patrols, according to information provided to Expressen.
"I can't confirm that, but it's been chaotic. We're filing a report for blue-light sabotage," says Sylvia Oldin.
A report of a violation of the Public Order Act is also being drawn up.
Earlier this week, the police flagged the possibility of a moped rally. Previous gatherings have seen high speeds and reckless driving. The police urged parents to talk about the risks involved.
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