Swedish police said Thursday clashes broke out at an Eritrean pro-government festival in a Stockholm suburb, as anti-government protesters trashed property at the site.
"Another public gathering took place close to the festival site, during which a violent riot broke out," police said in a statement.
Police added that they were at the scene in a suburb northwest of Stockholm and were "continuing their efforts to disrupt criminal acts and restore order".
Around 1,000 anti-government demonstrators authorised to hold a protest nearby broke through a police barrier and stormed the festival, the tabloid Expressen reported.
They tore down festival tents and used tent spikes as weapons against police as well as throwing stones at officers, the paper said.
An earlier police statement said there no reports of any injuries.
Footage from the scene showed cars and at least one tent on fire, sending large clouds of black smoke into the air.
Police shut down a section of the nearby E18 motorway in both directions as people fleeing the scene blocked the road.
The Eritrea-Scandinavia festival, which has been held for many years, features seminars, debates and lectures, as well as music, a bazaar and a fairground.
It is schedule to run from Thursday to Sunday.