"Up to now, already 28 foreign hooligans have been arrested following fights in Wroclaw's market square," Tomasz Siemoniak posted on X.

Wroclaw police spokesperson Wojciech Jablonski told AFP "a water cannon" was used to break up skirmishes between the rival sets of fans as part of central Wroclaw was sealed off.

According to Jablonski, "several hundred police officers intervened (...) to restore public order and identify those who broke the law".

Hundreds of Chelsea fans were inside the hastily erected security cordon.

"Police in riot gear surrounded a bar occupied by Chelsea supporters," an AFP journalist at the scene reported.

Chelsea fans jeered as riot police arrived to take up positions.

Police asked all "unauthorised" persons to leave the area.

Polish Prime Minister Donald Tusk promised "zero tolerance for violence on our streets".

He thanked the police for their "firm action against hooligans in Chelsea and Betis shirts in Wrocław. We warn: if necessary, the police will be even tougher today!" Tusk posted on X.

The city centre was filled with fans of both the English and Spanish clubs at the fanfest area, taking photos of the trophy in the build-up to the 1900 GMT kick-off.

The atmosphere in the old town was generally good-natured, the bars packed with supporters, with the occasional police sirens.

In Wednesday's final Real Betis are seeking their first European trophy while Chelsea are bidding to become the first club to win all five of UEFA's major men's club competitions.

The Blues have twice won the Champions League, Europa League, Super Cup and the defunct Cup Winners' Cup and can now complete the set if they overcome Betis in the final of Europe's newest competition.