A Hungarian camerawoman who caused global outrage after being caught on film tripping and kicking refugees as they fled police apologized Friday and said that she has received death threats.

"I panicked. I'm not a heartless, child-kicking racist camera-person," Petra Laszlo wrote in a letter to Hungarian newspaper Magyar Nemzet published on its website.

Disturbing footage emerged Friday of the way migrants are being treated inside Hungary's main refugee camp on the border with Serbia, with images showing families fed "like animals in a pen".

The video, shot secretly by an Austrian volunteer who visited the flashpoint Roszke camp on Wednesday, shows some 150 people wildly scrambling for bags of sandwiches thrown at them by Hungarian police wearing helmets and hygiene masks in a fenced-in enclosure inside a big hall.

Hungarian prosecutors said Thursday they had opened a criminal investigation for breach of peace against a camerawoman caught on film as she tripped and kicked migrants who were fleeing border police. 

In the footage, which sparked global outrage, Petra Laszlo can be seen tripping up a man sprinting with a child in his arms, and kicking another running child near the town of Roszke, close to the border with Serbia.

Austrian Railways on Thursday suspended services to Hungary as it struggled to cope with large numbers of migrants arriving from over the border.

"Because of the massive overcrowding of trains coming from Hungary, OeBB has to suspend train services to Hungary temporarily," the company said in a statement.

Footage of a Hungarian camerawoman shown tripping and kicking migrants as they fled police near Hungary's border has sparked global outrage.

A "Wall of Shame" page on Facebook featuring pictures, videos and commentaries linked to the incident involving journalist Petra Laszlo had gathered nearly 16,000 likes by Wednesday afternoon.

Some 400-500 migrants on Wednesday broke through police lines in Hungary near the main crossing point from Serbia, Agence France Presse reporters at the scene said.

The break-out took place near the flashpoint town of Roszke where migrants have to wait at a collection point before being taken to a nearby centre for registration.

Talking about imposing quotas on how many migrants each EU member state should take in is futile as long as Europe's outer borders are not secure, Hungarian Prime Minister Viktor Orban said Monday.

"The Hungarian standpoint does not exclude that at some point it will be possible to discuss a quota system in an intelligent and fair way," Orban said in a speech to foreign ambassadors in Budapest.

Austrian Chancellor Werner Faymann called Sunday for an emergency EU summit to resolve the migrant crisis, saying his country's admittance of thousands of refugees crossing from Hungary was just a "temporary" measure.

Migrants have been streaming into Austria from Hungary since Friday, after Hungary laid on buses and trains to take them to the border following days of confrontations with migrants who were barred by police from continuing their journey westwards.

EU foreign affairs head Federica Mogherini said the refugee influx, which has opened deep divisions in the bloc, is here to stay and member states must adjust to that new reality.

"It is here to stay; the sooner we accept it, the sooner we will be able to respond effectively (and) united as Europeans," Mogherini said after a two-day informal meeting of EU foreign ministers.

Hundreds of migrants stormed Budapest's main international station early Thursday after police re-opened it following a two-day standoff only to find that train services to western Europe had been suspended.

The main entrance was re-opened around 08:15 am (0615 GMT) and migrants burst in, rushing towards a train standing on one of the platforms, pushing, shoving and fighting with each other to get on board.