Police have clashed with protestors in Bern at an unauthorised demonstration against COVID-19 restrictions.

       Hundreds of people gathered in the Swiss capital on Thursday night despite warnings from the authorities.

       "There were clashes in the vicinity of the rally," Bern cantonal police said on Twitter.

       Fireworks were set off and objects were thrown at police officers, who responded with a water cannon, rubber bullets, and irritant gas.

       Thirteen people were taken into police custody, they added in a later statement. Seven of those arrested "had already attracted attention at similar demonstrations".

       The police also confiscated masking material and objects such as knives and screwdrivers. Those detained are facing numerous charges including violence and threats against police officers.

       "An increasingly heated and aggressive atmosphere was observed, which is why the authorities called in advance for people not to take part in the rally," the police added.

       Last week at a similar demonstration in Bern, protesters tried to force their way through a police barrier protecting the Federal Palace, the seat of Swiss government and parliament.

       Switzerland recently tightened its measures against COVID-19, making a health pass mandatory to enter a restaurant or bar, as well as museums, cinemas, and indoor sporting arenas.