Winter-like conditions are delivering a devastating blow to migrants and refugees trekking through the Balkans to escape war and hardships in their home countries.The combination of dropping temperatures and growing backlogs in processing people attempting to cross through nations such as Serbia and Croatia is creating a dangerous — and potentially deadly — environment for families trying to make their way deeper into Europe.Thousands of refugees and migrants have found themselves stuck at the border between Serbia and Croatia on recent nights, waiting for hours in the wind and cold for approval to move on, according to reports from the United Nations High Commissioner for Refugees (UNHCR) . Many lacked proper shelter and supplies to keep warm as the temperature dipped into the 40s.Aid workers in Serbia are seeing patients who are "soaked through and shivering but have nowhere to get warm [and] dry or change their clothes," Dr. Alberto Martinez Polis, Doctors Without Borders' medical activity manager in Serbia, said in a statement. At least 10 people have collapsed as a result of the harsh conditions."People are arriving here exhausted, hungry, and thirsty, and often in need of urgent medical attention," Riccardo Sansone, Oxfam’s humanitarian coordinator in Serbia, said via email. "They are traumatized and have often been abused by the smugglers and human-trafficking networks. Water and sanitation facilities are insufficient along the whole migration routes because Serbia was not expecting such numbers."The dangerous conditions have spurred action and calls for more help from humanitarian-aid efforts across the region. UNHCR distributed 460 blankets, 1,000 energy bars and 260 bottles of water, but said the current situation "is still a miserable wait and dangerous for the very young."

Oxfam International has also increased its response, launching a new push to provide essentials like coats, boots, toilets, and access to water.“Refugees are not prepared enough for winter,” Nahuel Arenas, Oxfam America's director of humanitarian response, told Refinery 29.Arenas recalled the story of one Syrian family that paid smugglers to take them from Turkey to Greece, then "had to throw everything away just to stay afloat in the boat." By the time the family made it to Serbia, "they had nothing. No clothes to change, [no] appropriate footwear," he said.Aid organizations are struggling to keep up with increasing demand for help, he said, due to funding shortages."Aid agencies have less than half the money required," Arenas said. "This means there are aid cuts. You either cut the quality of aid, or you decrease the quantity, or both. And this is what’s happening.”Historically, movement by migrants and refugees has slowed during the winter months, when the cold and conditions make the journeys more dangerous. But that trend has yet to take hold this year. The International Organization for Migration reported last week that 27,000 migrants entered Greece during the previous weekend — a total that exceeded figures seen during peak summer periods.Concerns that border closures and other measures restricting the flow of migrants and refugees will further complicate the path to central Europe — or close it — have created what one UNHCR official called a "rush, rush, rush," of people. "Many people think there is a window of opportunity, particularly with statements of politicians in Europe," Arenas said. "So I think that people don't want to miss that."Oxfam has been documenting the experiences of refugees and migrants as they move through Serbia. Click through to see their stories, along with captions provided by the organization.Editor's note: This slideshow has been updated to correct the surname of Oxfam America's director of humanitarian response and the photographer.