Violence and disorder has broken out in Glasgow city centre ahead of the Scottish League Cup final between Celtic and Rangers at Hampden Park.
Police Scotland said officers had dealt with a number of incidents on Saturday afternoon including missiles being thrown and windows smashed.
Videos on social media show large groups of football fans walking near Glasgow Central train station, followed by officers, before running down Argyle Street and letting off flares near shoppers.
The force has been authorised to use stop and search powers, including removing items being used to conceal identity.
The powers will remain in place until 21:00 in areas including the city centre and parts of the south side, east end and into South Lanarkshire.
In social media posts, large groups of fans can be seen walking to Hampden Park for the 15:30 kick-off.
Many in one group wore Santa hats, blue scarves and masks, while another group included many in dark green jackets and scarves over their faces.
In one clip, a crowd runs down Argyle Street – preventing people from leaving shops – as people are pushed to the ground and flares are let off.
A shopper told BBC News they were forced to take refuge in a nearby shop “for their own safety”.
Police Scotland said officers had been authorised to use stop and search powers under Section 60 of the Criminal Justice and Public order Act 1994.
This allows officers to stop people when appropriate and necessary, either in vehicles or on foot.
Ch Supt Steve Dolan said: “Officers have had to act swiftly and robustly to ensure public safety and reduce disorder.
“The use of weapons or violence will not be tolerated and officers will take action where necessary to ensure safety.
“It impacts other members of the public and the vast majority of football supporters who want to enjoy the cup final event safely. Officers will remain in the city as our operation continues and anyone with any concerns can approach them.”
