Rasul Orwani thought he had faced the worst after braving cold, rough seas in a rickety wooden boat to travel from Turkey to Greece, then came the Balkans.

After arriving in Macedonia with dozens of other migrants, the group crossed into Serbia on foot in the middle of the night, icy snow stinging their eyes and lacing the children's faces with tears.

Their heads bent low to protect from the cold, the migrants trudged slowly through the snow, carrying babies, small children and belongings along the 2-kilometer (1.2 mile) stretch of the road over the so-called green boundary between the two Balkan nations. A 10-year-old boy took a blanket from his shoulders to wrap it around his younger sister as they walked across the frozen landscape hand in hand.

Even as winter bears down on Europe and European Union countries set up new administrative hurdles for their entry, tens of thousands of migrants from the Middle East, Africa and Asia have been desperate enough to embark on the weeks-long journey across the Aegean Sea and along the so-called Balkan migrant corridor where frigid weather and stricter border controls have turned an already tough journey into an even more treacherous one.

Safe in the Serbian town of Presevo on the border with Macedonia, Orwani said there was no turning back.

"Our trip is very dangerous and risky," the 20-year-old Orwani said. "We crossed the sea, we were in a boat, and the waves in the sea could easily sink us in the water."

While Europe took in more than 1 million people in 2015, EU countries have been struggling to limit the biggest migration to the continent since World War II. Some countries along the migrant route have said they want to slow the influx or even completely block it. Some of the nations imposed new, stricter regulations for those transiting toward their ultimate goal, Germany or other rich west European countries.

As a result, dozens of refugees have been turned back from the borders amid freezing winter temperatures, while others have faced border closures and long hours in registration centers and refugee camps. Experts say the measures are unlikely to stop the flow, but could instead prompt the refugees to again start using illegal routes over razor-wire border fences and through forests, pushing them into the hands of ruthless smugglers.

Aid groups say migrants passing through the Balkans have faced difficulty traveling in the snow and ice, and there has been a surge in cold-related illnesses.

Women, children and babies, in particular, are in danger of hypothermia, according to the Save the Children aid group. It said migrants have been arriving in Serbia with blue lips, distressed and shaking from the cold. Exhausted mothers have told the group's aid workers they are unable to keep their babies warm and dry, and are stumbling while carrying them on the icy roads.

Saymira, from Afghanistan, crossed into Serbia with her husband and two young children just days before Orwani. Two months before her father and young sister died in the sea trying to reach a Greek Island from Turkey.

"Now I am very sad, I cannot tolerate this situation," she said while pushing a baby stroller through the snow on the border path between Macedonia and Serbia.

Saymira said she was on her way to Germany because she has relatives there.

Most refugees are not used to winter conditions, and many set off from home countries without warm clothing. Mirjana Milenkovski, the spokeswoman for the U.N. Refugee Agency in Serbia, said refugees are being provided heated shelter, bus transfers, warm drinks and clothes as they pass through Serbia and other countries.

From Serbia, migrants pack trains and buses to get to Serbia's border with Croatia. There, they again wait in refugee centers to head to another registration center in Croatia, where authorities go through the lists and check their refugee papers.

From Croatia, migrants go on to Slovenia and after more registration and checkups, they move on to Austria and then Germany. Dozens drop out along the way, with authorities in each of the countries conducting their own selection procedures.

The International Organization for Migration said 368 people died trying to cross the Mediterranean in January, nearly one in six of them children, as minors make up a growing percentage of those making the treacherous trip.

As Orwani made it to the Greek shores last month, dozens of others weren't so lucky. Two other unseaworthy boats carrying migrants sank, killing 46 people — many of them children — and highlighting the plight of people ready to risk their own lives and those of their children to start a new life somewhere free of war and poverty.

Macedonia, Serbia, Croatia and Slovenia first said they were letting in only people from war-ravaged Syria, Afghanistan and Iraq. New restrictions were imposed in January with only those seeking asylum in Germany or Austria being let through. This means all others are sent back from the borders, where they often seek smugglers' help to continue through clandestine routes.

Macedonia has recently started periodically closing its border with Greece, leaving thousands of desperate migrants stranded for days in a makeshift camp without any official word when they could continue their journey.

In addition, anti-immigration sentiment has been on the rise throughout Europe since the terror attacks in Paris in November and the New Year's Eve assaults on women in Germany. Austria said it will take 37,500 refugees this year and a total of 127,500 through 2019. Countries like tiny Slovenia have urged immediate EU action to control the flow — or even stop it completely on the Greek-Macedonian border — before the expected spring surge of asylum seekers when the weather gets warmer.

In the Presevo refugee center, Orwani was waiting patiently for his turn to register. He said he wanted to go to Germany, which — since he's from Afghanistan — means he might be allowed through. After crossing the Aegean Sea, Orwani said nothing else can be nearly as hard.

Orwani said he had never seen the sea until he boarded a small wooden boat in Turkey last month and set off with dozens of other migrants determined to reach Europe. The sea was rough and cold and Orwani's boat had engine trouble, barely making it to a Greek island. But, he says it was worth the risk.

"It was very dangerous, and our engine had a problem. We were frightened and it was really risky," Orwani said. "But, because we had such a bad situation (at home), we accept the risk."

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Gec and Dusan Stojanovic reported from Belgrade, Serbia.