Hundreds of asylum seekers have staged an angry demonstration outside Budapest's shuttered main international train station, demanding they be allowed to travel on to Germany, as a migration crisis puts the European Union's rules under unprecedented strain.

Key points: Station evacuated after 500 asylum seekers tried to board trains to Vienna

Station evacuated after 500 asylum seekers tried to board trains to Vienna Hundreds still waiting outside the station

Hundreds still waiting outside the station Europe receiving the biggest movement of people since WWII

Hungarian authorities closed the train station altogether, then reopened it but barred entry to the asylum seekers.

About 100 police wearing helmets and wielding batons guarded the station. Dozens of asylum seekers who were inside were forced out.

Sorry, this video has expired Asylum seekers protest outside Keleti train station in Budapest

Around 1,000 people waved tickets, clapping, booing and hissing, and shouting "Germany! Germany!" outside the station. Later they sat down, staring down at a police blockade at the entrance of the station.

The crowd later calmed down and several hundred people — men, women and children — remained outside in the baking sun, many sitting on the ground and in the streets around as police blocked entrances to the station.

"I am really pissed off. Why can't the Hungarians just let us go?" one Afghan asylum seeker, Haider, 31, said after ripping up his ticket.

"I worked as a translator for the US army for four years."

A public tannoy announcement was earlier made at the train station, which has been packed with asylum seekers for several weeks, that no trains would be leaving or arriving "until further notice" and asking everyone to leave.

Some of the people then began shouting as hundreds of police — some of them riot officers — began moving them out, although they offered no resistance and there were no clashes.

Hungarian railway authorities said they would allow "only those in possession of the appropriate travel documents and — if necessary — a visa to board trains travelling to western Europe".

Refugee rights group Hungarian Helsinki Committee warned the situation at the station was "very tense and unpredictable".

Riot police stand on the train track as they monitor asylum seekers. ( AFP: Attila Kisbenedek )

The tense situation came as the International Organisation for Migration (IOM) revealed over 234,770 asylum seekers have landed in Greece alone this year, more than the whole Europe-wide figure of 219,000 for all of 2014.

At least 2,600 died on the hazardous journey, drowned or suffocated in dangerous or unseaworthy boats, it added.

Another 114,276 made it to Italy, with most of the other arrivals split between Spain and the island of Malta.

UN children's agency UNICEF said eight out of 10 refugees arriving in Macedonia, one of the main transit points onto western Europe, were fleeing war-torn Syria.

An estimated 100,000 have passed through the Balkan country since June, it said.

A third of them were women and children, and one in every eight women was pregnant, it added.

The arrival of hundreds of thousands of asylum seekers has confounded the EU, which has no border controls for travel between 26 countries of its Schengen area but requires those seeking asylum to remain in the country where they first arrive until applications are processed.

Frustrated asylum seekers, pouring into Hungary at a rate of more than 2,000 per day during August, were left to set up ever-growing makeshift camps outside the two main stations in Budapest.

A total of 3,650 people — lots of young men but also large numbers of families with small, exhausted children and a few old people — reached Vienna by train on Monday, this year's biggest daily number, Austrian police said.

Spain's prime minister described the record influx as Europe's "greatest challenge" for the coming years.

"What we're seeing now is the greatest challenge for Europe in the coming years, I have no doubt about that," Mariano Rajoy said during a visit to Berlin.

The crisis has prompted the government in Budapest to reinforce its border with a razor wire fence and deploy thousands of extra police to try to funnel the flow of asylum seekers to legal channels rather than allowing them through unchecked.

Asylum seekers stand in the Eastern (Keleti) railway station of Budapest behind of a line of the local police on August 31, 2015. ( AFP: Attila Kisbenedek )

Biggest movement of people since WWII

Europe is on the receiving end of the biggest movement of people since World War II, with more than 300,000 arriving this year, many fleeing war, persecution and poverty in the Middle East and Africa.

The escalating crisis has divided the 28-member bloc ahead of fresh emergency talks on September 14, with Western European leaders calling for more efforts to help the new arrivals while countries on its eastern borders say they are struggling to cope.

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In a show of support for the asylum seekers, 20,000 people took to the streets of Vienna on Monday to protest their ill-treatment, while senior government officials attended a church service for 71 asylum seekers found dead in an abandoned truck last week.

Hungary's government criticised Berlin's easing of asylum rules — aimed at relieving pressure on southern European nations where asylum seekers arrive by sea — as "[building] up the hopes of illegal immigrants".

Under current EU regulations, known as the Dublin provision, asylum seekers must remain in the first European country they enter while their application is being processed.

Those who subsequently travel to other member states face deportation back to the EU country they originally entered.

Hungary has become a frontline country for asylum seekers arriving via the western Balkans as they flee war and unrest in the Middle East, Africa and Asia.

The Hungarian government on Monday demanded that Berlin clarify "the legal situation, in order to eliminate this ambiguity and controversy".

"It is in our common interest that all member states abide by EU legislation. Order and legality must be restored at the borders of the European Union," said government spokesman Zoltan Kovacs.

AFP/Reuters