Footage has emerged of migrants being thrown bags of food at a Hungarian camp near the border with Serbia.
An Austrian woman who shot the video said the migrants were being treated like “animals” and called for European states to open their borders.
The emergency director of Human Rights Watch said the migrants were being held like “cattle in pens”.
It comes as Central European ministers again rejected a mandatory quota system for sharing out migrant arrivals.
“We’re convinced that as countries we should keep control over the number of those we are able to accept and then offer them support,” Czech Foreign Minister Lubomir Zaoralek said at a press conference with his Hungarian, Polish and Slovak counterparts.
The European Commission, with Germany’s backing, wants 160,000 asylum seekers a year to be shared out between EU members.
The Central European states had already rejected the plan, even though they would take in far fewer refugees than Germany if the EU backs the proposals.
In recent weeks, tens of thousands of migrants have been desperately trying to make their way to Europe from war-torn Syria and Libya. Many of them travel through Hungary to Germany, Austria and Sweden – wealthier EU nations with more liberal asylum laws.
Hungary in particular has become a key point on the journey north for the migrants, with more than 150,000 people arriving this year.
The footage from Hungary comes from a camp at Roszke, one of the bottlenecks where large numbers of migrants heading north and west have built up.
It was filmed by Michaela Spritzendorfer, the wife of an Austrian Green party politician who was delivering aid to the camp, and Klaus Kufner, a journalist and activist.
“These people have been on a terrible tour for three months,” Ms Spritzendorfer told the BBC.
“Most of them have been across the sea now and on the boat and through the forest and they’ve gone through terrible things and we, as Europe, we keep them there in camps like animals. It’s really a responsibility of European politicians to open the borders now.”
The lack of support for migrants in Hungary has drawn criticism from activists. Peter Bouckaert, emergency director at Human Rights watch, described the situation at Roszke as “inhumane”, saying that migrants were held like “cattle in pens”.
At the scene: Anna Holligan, BBC News
The Hungarian refugee camps have become humiliating holding zones for the thousands trying to cross the country’s borders. Journalists are banned from entering, but images shared by human rights groups and refugees are disturbing.
The Hungarian government has not yet commented, but the images will fuel the allegations that Hungary is failing to meet the minimum standards for the treatment of migrants, as laid out in the European Convention on Human Rights.
The Council of Europe has reminded member states that people should not be treated like prisoners.
Many of the people I’ve spoken to, from Raqqa, Idlib and Homs have become numb to violence in Syria, but their treatment in what is supposed to be a place of refuge is hard to bear.
The UN’s refugee agency, UNHCR, said it was sending 300 pre-fabricated housing units to Hungary.
There is also a bottleneck at Hungary’s border with Austria. Officials said about 8,000 people had crossed into Austria at Nickelsdorf on Thursday and a similar number were expected on Friday.
Existing shelters in the area are full and the army is putting up tents, the BBC’s Bethany Bell reports. Exhausted men, women and children are everywhere, some even sleeping on the manicured gardens of Nickelsdorf’s neat houses.
With no buses running, and just one packed train departing, some have started walking along the motorway towards Vienna, which police have closed to traffic.