BELGRADE, Serbia (AP) — It was a week in frigid hell for hundreds of migrants squatting in an abandoned warehouse in the Serbian capital of Belgrade while trying to move on toward Western Europe.

When the weather suddenly turned nasty before Orthodox Christmas Eve on Jan. 6, temperatures plummeted way below 0 C (32 F) and a cold wind pushed into every corner of the makeshift migrant shelter.

Men and boys occupying the sprawling complex — a vast crumbling building with few windows or doors — found themselves in danger of exposure while aid groups scrambled to help.

Wrapped in blankets, migrants huddled next to each other, desperately trying to warm up by the fires they lit inside and outside the warehouse.

A search for firewood became a morning routine — migrants chopped branches from frozen trees or burned old wooden railway tiles they picked from the abandoned tracks by the warehouse.

Thick, choking smoke filled the warehouse. Migrants said two people have been hospitalized with respiratory problems from inhaling the smoke.

Muhammad Yusuf Navid from Afghanistan said he couldn't sleep at night: "It is too bad, too cold. I did not sleep for one hour."

At lunchtime every day, hundreds of migrants lined up, with a blizzard brushing wind and snow against their faces, to receive a warm meal distributed by aid groups.

Holding plastic dishes, the men looked for a quiet corner or squatted in the snow to eat the meal of cooked cabbage or beans. Some melted the snow to wash themselves despite the freeze.

Migrants appealed to European nations to open their borders — graffiti on one wall of the Belgrade warehouse reads: "The problem is borders."

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Darko Vojinovic is The Associated Press' chief photographer in Belgrade. Follow Darko Vojinovic on Twitter: https://twitter.com/apdarkov