At least 29 newborns and children have reportedly died over the past two months while heading to a Syrian refugee camp or not long after getting there, the World Health Organization (WHO) said Thursday. Most of them died from hypothermia as they joined tens of thousands of people seeking safety during Syria's winter.

Many of the roughly 23,000 people who recently went to the Al-Hol camp in the country's northeast have traveled in open trucks -- or on foot -- in frigid temperatures, according to WHO. Long security screenings in an open field have prolonged some of their journeys.

Distressing conditions have awaited those who finally arrived. There is no heat in the Al-Hol camp, which is also short of toilets, tents, health care services and sanitation facilities. Security restrictions and bureaucratic hurdles are hindering humanitarian access, WHO said.

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"Thousands of new arrivals have been forced to spend several nights in the camp's open-air reception and screening areas, without tents, blankets or heating," the United Nations agency said.

WHO called the situation heartbreaking and critical, and said it is "extremely concerned" about the camp's "deteriorating humanitarian situation." In less than eight weeks, the number of people at the camp has ballooned from 10,000 to nearly 33,000 as Syrians flee fighting in a nearby region.

"The authorities are overwhelmed and struggling to cope with the sheer numbers of people," WHO said. "Many new arrivals are malnourished and exhausted following years of deprivation living under the control of the Islamic State of Iraq and the Levant," it said, referring to ISIS.

Since Syria's conflict started in 2011, more than 5.6 million people have fled the country and 6.6. million have been internally displaced, according to the U.N. refugee agency. More than 13 million people in the country are in need as the conflict continues.