The man, whose name was not released, suffered serious head injuries when he was attacked around midnight Saturday (2200 GMT) by between 30 and 40 people outside a bar where ice hockey fans tend to hang out, Zurich police said in a statement.

Police launched an investigation and questioned a number of people but had yet to determine who the assailants were or why they had suddenly attacked the man, the statement said, calling for more witnesses to come forward.

The victim himself was in critical condition and had not yet been questioned, police told the ATS news agency.