Hundreds of migrants have arrived by rail in the Austrian capital Vienna after being held for several hours at the Hungarian border.

Many of them immediately boarded trains bound for Germany.

Austria has also introduced extra checks on road vehicles entering from Hungary after 71 dead people were found in a lorry on Thursday.

The number of migrants entering Europe has reached record levels, with 107,500 arriving in July alone.

Most of those found dead on Thursday, on the A4 at Parndorf, were thought to be Syrians fleeing the country's civil war.

Five people have been detained in connection with the deaths.

Thousands of people rallied in Austria on Monday demanding better rights for migrants.

As well as the bodies in the lorry in Austria, hundreds more people drowned in the Mediterranean last week while trying to reach Europe from Libya.

On Monday, Austrian authorities had stopped trains heading for Vienna from the Hungarian capital Budapest, saying they would turn back anyone on board who had made a request for asylum in Hungary - but it is not clear if this actually happened.

Austria's rail service OeBB said the route from Budapest was facing severe disruption due to "overcrowding".

Austrian police said up to 1,000 people arrived in Vienna's main railway station on Monday, and were met by volunteers handing out food and drink.

Once in Austria, migrants would have two weeks to decide whether or not they wanted to claim refugee status there, police said.

'No police, no problem'

The BBC's Bethany Bell in Vienna says Germany is the main destination for migrants arriving on the EU's eastern borders.

Germany expects to take in 800,000 migrants this year - four times last year's total.

Among them is Khalil, 33, an English teacher from Kobane in Syria who was travelling with his wife and sick daughter through Austria to Hamburg.

"Thank God nobody asked for a passport," he told Reuters news agency. "No police, no problem."

Austrian police said five suspected people smugglers had been arrested as part of its checks on vehicles entering from Austria. More than 200 migrants had also been found as part of those checks.

The Austrian checks appear to undermine the EU's Schengen system, which normally allows unrestricted travel. But in exceptional circumstances countries can reintroduce border controls under Schengen.

Austria's interior ministry told the BBC that the checks would not be necessary if there were an agreement to distribute the migrants fairly.

Meanwhile, German Chancellor Angela Merkel called for greater EU co-operation on the issue and implicitly called for other countries to welcome more refugees.

"If Europe fails on the question of refugees, then it won't be the Europe we wished for," she said on Monday.

But she said there would be "no tolerance for those who question the dignity of other people" after a spate of arson attacks on refugee shelters and anti-migrant demonstrations.

Mrs Merkel's call for greater co-operation was echoed by French Prime Minister Manuel Valls, who warned that Europe's migrant crisis would be a "long and difficult challenge".

The UN says the continuing conflict in Syria is a major factor behind the rise in migrant numbers.

Greece, Italy and Hungary have particularly struggled with the surge of migrants from not only Syria but the rest of the Middle East and Africa.

An extraordinary meeting of EU interior ministers is to be held on 14 September.

Some governments have refused to take in refugees and resisted EU proposals to agree on a common plan.

Others are tightening their policies on asylum and border security, sometimes because of rising anti-immigration sentiment.

Source: BBC