MIRATOVAC, Serbia (AP) — In a new human wave surging through the Balkans, thousands of exhausted migrants from the Middle East, Asia and Africa crossed on foot Monday from Macedonia into Serbia on their way to Western Europe.

The rush over the border followed Macedonia's decision to lift the blockade of its border with Greece, after thousands of migrants stormed past Macedonian police who tried to stop their entry by force.

Some 7,000 migrants, including many women with babies and small children mostly from Syria, crossed into Serbia over the weekend by Monday morning. Some were pushed in wheelchairs and wheel barrows or walked on crutches. Hundreds more entered Macedonia from Greece on Monday.

On Monday, there were more scuffles between Macedonian police and the incoming migrants on the border with Greece. The police were gradually letting into the country only small groups of migrants, trying to prevent their rush. A pregnant migrant from Aleppo, Syria, was slightly injured in the scuffle.

In Austria, police said 37 people were injured — seven seriously — when two vans packed with migrants collided Monday near the Hungarian border. Police dozens more migrants fled, along with the suspected smugglers.

The new migrant tide that has hit the Western Balkans has worried EU politicians and left the impoverished Balkan countries struggling to cope with the humanitarian crisis.

Visiting Macedonia on Monday, Austria's Foreign Minister Sebastian Kurz talked to migrants and shook hands with them. He also said Greece needed to control its borders more effectively.

"This is a humanitarian disaster, this is a real disaster for the whole European Union and I think there is the real need to have more focus on this problem, not only on the route through Italy but also on the route on the Western Balkans," Kurz said.

A man from Syria, Imad Shoumali, told Kurz that migrants have no choice but "to come here, to find safe zone, to find good future for us, for our family, for our kids."

"We lost everything in Syria, you have to help us to finish the war in Syria," he said. "If you finish now I am back from this point, directly. I don't like to come to Europe."

After entering Serbia, the migrants, fleeing wars and poverty, head toward EU-member Hungary from where they want to continue further north to richer EU countries, such as Germany and Sweden.

After they formally ask for an asylum, migrants have three days to reach the border with Hungary which is rushing to build a barbed wire fence on its border with Serbia to block the migrants.

Greece's coast guard was searching for at least five people missing at sea after the dinghy they were using to cross from Turkey overturned off the coast of the eastern Aegean island of Lesbos.

The coast guard said it had rescued six people and recovered the bodies of two men, and was searching the area for the missing. The two told authorities they had been in a boat carrying about 15 people when it overturned.

Greece has been overwhelmed by an influx of mainly refugees reaching its islands from Turkey.

The Greek coast guard said it had picked up 877 people in 30 search and rescue operations from Friday morning to Monday morning near the islands of Lesbos, Chios, Samos and Kos. The figures do not include the hundreds that manage to make it to the islands themselves, mostly in inflatable dinghies.

Kurz noted that under EU treaties, known as the Dublin accords, asylum- seekers are supposed to apply for asylum in the first EU country they reach. Greece and Italy, where nearly all those seeking to enter the EU arrive, argue that this places a massively unfair burden on countries on the EU periphery.

"I think there's a need for border control, at least on the outlines of the European Union. And the second point is, it's also the fault of Greece if there is no support for the refugees there," Kurz said.

Amer Cohadzic in Gevgelija, Macedonia, Elena Becatoros in Athens, Jovana Gec in Belgrade, Serbia, and George Jahn in Vienna contributed to this report.