Austria has closed the A4 motorway near the Hungarian border for security reasons as scores of migrants walked to Vienna, said police.

Reporters estimate 1,000 people pushed through police cordons to make the 40-mile trip on foot on Friday, although it is unclear why they are not using trains.

Trains having been taking thousands of migrants and refugees from the Hungary border to Vienna for days with most heading on to Germany and other West European countries.

Some 8,000 people crossed the border into Austria on Thursday and 3,600 had already made their way across since midnight. 

Police spokesman Gerhard Koller said 1,500 people had spent the night outdoors.

Austria's railway company, OeBB stopped its rail service from and to Hungary due to overcrowding of trains and platforms and is due to decide within hours whether to reopen it again.

Meanwhile, US President Barack Obama has directed his administration to prepare to take in at least 10,000 Syrian refugees over the next year.

Since the start of the Syrian civil war in 2011, the United States has taken in 1500 refugees, with 300 more expected to be cleared by October.

Some 22,500 refugees and migrants arriving on the Greek island of Lesbos have been registered by officials since Monday evening according to police.

Lesbos is one of several Greek islands in the Aegean Sea that have been struggling with a huge influx of people setting sail from Turkey, many of them Syrian refugees.

Authorities opened an emergency registration centre on the island on Monday evening to clear a huge backlog.

As the crisis continues, refugees trying to get into Macedonia from Greece have been beaten by border police.

Torrential rain has also been making an already difficult situation even worse.