AUSTRIA and Germany have thrown open their borders to thousands of exhausted asylum seekers, bussed to the Hungarian border by a right-wing government that had tried to stop them but was overwhelmed by the sheer numbers reaching Europe's frontiers.

Left to walk across the border into Austria, the asylum seekers, many of them fleeing war in Syria, were then whisked by train and shuttle bus to Vienna and then on by train to Munich and other cities in Germany.

By early evening Saturday, about 6,000 had arrived in Munich and nearly 2,000 more were expected on two trains due after midnight.

Clapped and cheered as they disembarked, new arrivals queued at registration tents to be screened, fed and clothed. Most were set to stay in Munich, although more trains were due to take 800 people to Dortmund and 460 to Frankfurt on Saturday evening.

Austrian police said more than 6,000 people had entered the country by noon with more expected in what has become Europe's most acute humanitarian crisis since the Yugoslav wars of the 1990s.

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