BERNE, Switzerland (AFP) - Swiss police said Sunday they had arrested 61 people in clashes at a politically-charged techno parade in Berne, which the authorities said left 21 members of the security forces injured.

Trouble erupted in Berne's picturesque Old Town in the early hours of Sunday during the unauthorised "Tanz Dich Frei" (Dance Yourself Free) parade.

After a standoff between riot police and dozens of masked and hooded "Black Bloc" hardliners, an AFP reporter saw a group attempting to break down temporary barriers protecting parliament.

Police responded with tear gas and a water cannon which sent the crowd scattering across the square, as a helicopter circled overhead.

Some protesters held their ground, pelting police and the water cannon with bottles, fireworks and flares.

Police put the number of participants in the parade at 10,000, and said the vast majority were peaceful.

Braving rain and unseasonably chilly weather, the eclectic crowd had snaked through the Swiss capital among trailers carrying huge speakers that pumped out dance beats.

Hardliners spraypainted and smashed windows of banks, shops and the Swedish embassy, which was on the parade route, before small groups fanned out in the city centre to skirmish with police and target other buildings, looting shops.

An initial estimate put the damage at several hundred thousand Swiss francs, police said.

Ambulance workers were called out at least 50 times, mostly due to heavy drinking in the crowd.

Tanz Dich Frei was organised by an anonymous collective which mustered participants on Facebook.

In a statement posted on their page Sunday, the organisers lashed out at the authorities, saying many protesters had acted in self-defence and that city officials had conducted a smear campaign.

"The state made its intentions clear. The protection of parliament was more important than that of thousands of people," they said.

Ahead of the event, organisers had appealed for the violent few to stay away.

"It's a pity the event couldn't pass off peacefully," they said Sunday.

The parade, now into its third year, is tolerated grudgingly by city authorities even though the organisers lack a permit.

The organisers say that the right to party is just one cause, along with opposition to the gentrification of parts of Berne where the alternative scene used to thrive, which they claim has driven up property prices and created a sanitised city for the rich.

They also push an anti-capitalist message, blasting neo-liberal economics and heavyhanded policing.

The 2012 edition drew some 20,000 people. Berne's population is around 126,000.

After trouble last year, Berne police were bolstered by forces from other cities.

They have been stretched not only by the techno protest but also last trouble at last Monday's Swiss football cup final, the security operation for last Friday's visit by Chinese Premier Li Keqiang, and are bracing for a high-tension football league match on Wednesday.