Around 80,000 Manchester United and Tottenham supporters have descended on Spain ahead of the Europa League final, despite the San Mames stadium in Bilbao having a capacity of just 52,114.
Spanish media have criticised fans for being "difficult to control" amid reports of clashes between rival supporters.
Both clubs received allocations of only 15,000 tickets each, but thousands of ticketless fans have still travelled to the city.
Spanish news agency EFE reported on Tuesday that "some fans are already losing control" in the streets of central Bilbao, despite the deployment of 2,000 police officers.
Fans are causing havoc in Bilbao
Reuters
Supporters have been pictured climbing on traffic lights, with Bilbao-based newspaper El Correo reporting that Tottenham fans had "destroyed two traffic lights" and "raised them like a trophy".
Tottenham supporters gathered in Pozas near the stadium, while Manchester United fans congregated in Plaza Nueva. Several United fans reportedly punched another supporter in Plaza Nueva, requiring intervention from eight police officers.
In another incident, Tottenham supporters were claimed to have showered rivals with beer, while one fan was pictured vomiting in the street.
A fan zone in El Arenal was reported to be calm with a large police presence.
JUST IN: Lewis Hamilton warns of 'difficult' Monaco weekend as race to expose major 'weakness'
Footage on Tuesday night showed supporters clashing in San Sebastian, 48 miles away from Bilbao.
According to Spanish publication El Diario Vasco, the situation escalated around 9.20pm local time, beginning with shouts and insults before a punch caused one fan to fall to the ground.
Witnesses reported that fans began throwing objects and overturning tables before police arrived and remained in the area.
An ambulance was dispatched to treat those affected, but after a few minor treatments, it was reportedly not deemed necessary to take anyone to hospital.
READ MORE: Rudd Van Nistelrooy set for Leicester City exit as replacement set to be announced in days
There are thousands of ticketless fans in Bilbao
A police spokesman confirmed on Wednesday morning that no arrests have been made in either Bilbao or San Sebastian despite the reported incidents.
"In relation to the incidents arising out of the celebration of the Europa League final we have no information on any serious occurrences," the spokesman said.
"No one has been seriously injured and there have been no arrests so far."
LATEST SPORTS NEWS:
The spokesman acknowledged the fight in San Sebastian's Old Town, adding: "That incident didn't lead to any arrests."
The Basque Government had previously activated a "protection plan" to monitor the situation and respond to potential emergencies.
Both Manchester United and Tottenham fans have travelled to Bilbao hoping their teams can rescue what have been dismal seasons by securing European glory.
The two clubs head into the final amid disappointing Premier League campaigns, with both sides languishing in 16th and 17th place in the table.
There is disruption all over Bilbao
Reuters
Victory would be particularly significant for Tottenham, who would end a 17-year trophy drought with a win.
The match carries the added incentive of Champions League qualification for next season, making the final reportedly worth around £100million to whichever of Ruben Amorim or Ange Postecoglou's sides emerges victorious.
