Thousands of people hoping for asylum in western Europe are trekking to Vienna from Austria's main border crossing point with Hungary after rail traffic was suspended due to overcrowding.
Austrian Federal Railways said it no longer has the capacity to deal with the thousands of people at the Nickelsdorf crossing wanting to board trains to the Austrian capital.
Once in Vienna, most have travelled on to Germany and other western EU nations.
Rail services between Vienna and the Hungarian capital Budapest were suspended yesterday. With no trains running, thousands of people set out on the major road linking the Nickelsdorf border crossing with Vienna, 40 miles away.
Police official Hans Peter Doskozil said 7,500 people crossed into Austria at Nickelsdorf on Thursday.
Meanwhile, thousands more refugees endured torrential rain as they crossed from Greece into Macedonia.
About 7,000 people made their way past police in camouflage jackets as they contended with poor weather and muddy conditions.
The sudden onset of autumn took tens of thousands by surprise along the Balkans route from Greece to Hungary, the main gateway to western Europe for more than 160,000 asylum seekers from Syria and elsewhere already this year.
As recently as last week, those making the epic journey, much of it on foot, were baking in a region-wide heatwave and free to sleep under the stars.
Now they are without shelter and struggling to keep camp fires burning, highlighting the inadequate support provided by several European governments at each border crossing.
Conditions rapidly deteriorated on Hungary's southern border with Serbia, where about 3,000 people crossed at an approved rail site, or illegally by ducking under the barbed wire marking the frontier.
With Hungary and other nations providing few facilities on their borders, travellers have poured into the few tents erected by relief workers trying to compensate for the lack of government support.
Medics gave first aid to several mothers and their children and covered them with thermal blankets.
International aid workers said Hungary has failed to provide sufficient shelter at migrant bottlenecks on the border, particularly near the village of Roszke.
The country instead is investing in a new security regime, due to begin on September 15, designed to close its border with Serbia backed by more than 3,000 troops, many of whom conducted drills on Thursday in co-operation with Serbian colleagues.
Elsewhere, the governor of Greece's northern Aegean region said authorities had managed to register 20,000 refugees and migrants on the island of Lesbos in the space of three days, significantly easing the overcrowding on the island.
Regional governor Christiana Kalogirou told private Skai television the number of refugees and migrants on the island had reached about 30,000. Greece's caretaker government, appointed about two weeks ago to lead the country to elections on September 20, sent extra staff to speed up registration and chartered two extra ferries to help move people to the mainland.
More than 250,000 people have reached Greece this year, the vast majority arriving on islands from the nearby Turkish coast. About half of all those who arrive do so on Lesbos. Few, if any, want to remain in financially stricken Greece.
The UN refugee agency said it is deploying hundreds of prefabricated homes to central and south-eastern Europe to temporarily house some of the refugees.
Spokesman William Spindler said UNHCR is stepping up its operations in Europe amid what it estimates is an influx of more than 380,000 people across the Mediterranean so far this year. The International Organisation for Migration has put the figure at more than 432,000.
Mr Spindler said "trucks are on the way" after the Geneva-based agency won government approval to send 300 prefabricated homes to provide temporary housing to refugees awaiting registration by authorities.
He said UNHCR is also sending supplies and blankets for 95,000 people in the four countries among the most affected: Hungary, Serbia, Macedonia and Greece.