Syrian immigrants walk on a railway track after they crossed the Hungarian-Serbian border near Roszke, Hungary August 25,2015. [Photo/Agencies]

With frequent attacks on refugee shelters and warnings of rising intolerance of foreigners, Merkel's cabinet agreed to double the funding this year to help towns cope with the record number of arrivals.

Hungary, which is part of Europe's Schengen passport-free travel zone, is building a 3.5-metre high fence along its 175-km (110-mile) border with Serbia, taking a hard line on what right-wing Prime Minister Viktor Orban says is a threat to European security, prosperity and identity.

Government spokesman Zoltan Kovacs said parliament would debate next week whether to employ the army in the border effort.

The numbers travelling through the cash-strapped Balkans have soared in recent weeks, with 3,000 crossing into Macedonia daily from Greece.

The chief commissioner of Hungarian police, Karoly Papp, said police were readying six special border patrol units of an initial 2,106 officers, equipped with helicopters, horses and dogs, to be sent in depending on the situation on the Serbian border.

"They don't have and will not get an order to shoot," Papp told a news conference.

In Roszke, the police spokesman said some 200 migrants at the reception centre where unrest flared had refused to be fingerprinted, fearing that, as per EU rules, if they are stopped later elsewhere in the EU they will be returned to Hungary as their official point of entry.