Ugly scenes erupted in Hungary as refugees fought their way onto what they thought was the first train to western Europe in days, only to be left feeling tricked as police halted the train and tried to move them to a refugee camp.

Mayhem ensued at the small train station of Bicske where it was stopped, including when one man pulled a woman and a baby onto the train tracks and refused to be moved before several bulky police dragged him off.

"I would rather die than go to a camp," one Iraqi man told AFP as his daughter - one of many children on the train - was taken to hospital with a swollen cheek in the humid autumn heat.

Most of the migrants, estimated by an AFP reporter to number 200-300, refused to get off the train and onto buses that state news agency MTI reported would take them to the nearby camp.

Furious at their treatment and feeling they had been tricked onto the train, they began chanting "Germany! Germany!" - their intended destination after a treacherous journey of hundreds of miles.

Others held placards with the words "SOS" and "Help!".

"I need to go to Germany for life," read another, held by a child. Police handed out water bottles but some of the migrants poured the water onto the ground in disgust.

There were around 100 police present including riot police.

An AFP reporter said late afternoon that reinforcements were arriving.

The incident occurred after Hungarian police decided on Thursday morning to open Budapest's main international train station Keleti, two days after blocking it to migrants.

That decision came after Hungary on Monday allowed several thousand to board trains for Austria and Germany.

It left around 2000 men, women and children stranded around the station or in the underground "transit zone", sheltering on blankets in cramped conditions, looked after only by Hungarian volunteers.

As well as the crowds at Keleti, several hundred migrants have been camping out at nearby John Paul II square, as well as another train station, Nyugati (western), across the city.

"I want to know when the Hungarian government is going to let us go to Germany," said Nizamuddin, 31, an Afghan who worked as an interpreter for the US army for four years and who wants to claim asylum in Germany.

"I slept for about two hours last night. It was very cold and windy last night and I had no blanket. My body was shaking," he said at the Keleti station.

"I last showered four days ago. I haven't changed my shirt for four days and my trousers for 15 days. Smugglers took my bag and my mobile phone."