As temperatures drop close to zero and rain pours down, families in and around the country's capital are moving into unheated schools, mosques and half-finished buildings to try to escape.
Ettie Higgins, UNICEF's deputy representative in Syria, says it's a heartbreaking situation, with 500,000 Syrian refugees spread across the region and four million Syrians affected by the war between President Bashar al-Assad's regime and rebel groups.
"They have hundreds of thousands of [internally displaced persons] living there in semi-finished apartment buildings," in Adraa, outside Damascus, Higgins said.
Much of the attention so far, she says, has gone to Syrian refugees outside the country.
"There's also a massive crisis within Syria that we need to be able to respond to," Higgins said.
"Every little bit counts — even if [people] think it's just a small amount, it will make a huge difference in a country where they're running out of bread, there's no fuel and there's no wheat either to make the bread."
Yesterday alone, UNICEF distributed supplies to 23,000 people. That includes blankets, winter clothing, hygiene kits with items like shampoo and toothbrushes, diapers and emergency food kits that include high-energy bars.
Families are streaming into Damascus from areas around the capital. The past week has been particularly bad because of intense fighting in the Palestinian refugee community of Yarmouk, Higgins said, describing a man who walked five kilometres with his nine-year-old daughter.
"He had left Yarmouk camp at 5 a.m. in the morning because they had been taking shelter in the camp all night and the fighting had raged through the night. At 5 a.m., he took his daughter and he said we're leaving," Higgins said.
"He has already lost his wife, she was killed by a mortar.... He just said he had nothing left anymore. He was just sitting on the ground exhausted. They didn't have anything except the clothes on their backs."
Higgins has been in Syria since August. The situation is getting more severe, she said.
"Before, you would have been able to keep outside and you wouldn't have got hypothermia and your kids wouldn't be getting pneumonia if you slept outside for a night or two. But now the temperatures are getting bitterly cold, especially in the north where snow falls as well," she said.
On top of everything else, it's rained as much in the past day as it has in the last four years, Higgins said.
There are 200,000 thermal blankets en-route, with another 50,000 arriving next week on a ship from Pakistan.
UNICEF is also trying to set up toilets and distribute trash cans to keep the more urban areas clean and ward off disease. More than 1.1 million children have been immunized against measles and 1.4 million against polio.
The UN is appealing for $500 million to help the estimated two million displaced people inside Syria who have been driven from their homes as violence spreads throughout the country.
The United Nations also launched a $1-billion pre-Christmas emergency appeal Wednesday to help refugees who have fled Syria.
The UN wants to stave off the threat of the cold in neighbouring Jordan, Turkey, Lebanon and Iraq.