Around 100-150 migrants staged a demonstration outside Budapest's main international train station Wednesday as police blocked some 2,000 people from boarding trains to Austria and Germany, an AFP reporter said.

Around 600 men, women and children, mostly from Syria, Iraq and Afghanistan, were sitting or standing outside the Keleti station while some 1,200 were downstairs in a so-called "transit zone".

Meanwhile around 100 migrants arriving from a registration centre near the border with Serbia were sitting on the platform at a suburban train station, refusing to board a train to the Debrecen refugee camp.

Police said in a statement that the group "demanded to be allowed to travel on to Germany... Police have taken the necessary security steps to ensure that train traffic is undisturbed."

Hungary, which saw 50,000 migrants enter the country in August alone, this week allowed thousands to board trains to Austria and Germany but in a U-turn on Tuesday police suddenly blocked access to the station for anyone without an EU visa.

Only around 150 migrants arrived in Vienna by train from Budapest on Tuesday afternoon, police said. On Monday a record 3,650 arrived.

The Hungarian government of right-wing Prime Minister Viktor Orban, which has built a razor-wire barrier along its 175-kilometre (110-mile) border with Serbia, said that it was applying EU rules.

"Normal people, abnormal people, educated, uneducated, doctors, engineers, any people, we're staying here. Until we go by train to Germany," said Mohammad, a Syrian protesting at the station.

"And this is what we will be doing (protesting) for the next day, for the next month, for the next year and for our whole life. We need our rights... It's not our dream to stay here and to sleep in the streets."

Hungary's razor-wire barrier is proving ineffective in keeping out the tens of thousands of people trekking up from Greece through the western Balkans, with Hungarian authorities saying that 2,284 crossed on Tuesday including 353 children.

"If Europe is letting us in, why don't they give us visas? Why do we have to make this clandestine journey?" Bilal, a Syrian from the divided city of Aleppo, told AFP on Tuesday near Serbia's border with Hungary.

"We fear that one day everything will change, that even Germany will close the border when it has had enough, so we must make our journey extremely fast," he said.