“Schengen is under threat. Schengen most definitely could fall apart and probably will fall apart if we do not get a common European policy in respect of migration.” UN special representative Peter Sutherland said at a news conference on the refugee crisis in Geneva.
The agreement - implemented in 1995 - abolished border controls between 26 European countries, most of which are EU members but not all.
Chaotic scenes in Hungary in recent days have seen thousands of refugees attempting to pass through the EU nation to reach mainly Austria and Germany. Hungary initially attempted to prevent them from crossing its borders but later relented, leading to questions about the nature of a border-free Europe.