Supporters were seen on video footage trying to break through security gates and using barriers as weapons.
Bottles were also thrown in the clash, with many of the fans wearing flags representing their countries.
One topless fan was seen being confronted by two members of security personnel.
It is not known at this stage what started the violence.
There are also reports that a plane flying a political banner was seen travelling over the stadium.
West Yorkshire Police have been contacted for comment.