Tens of thousands of civilians evacuated from besieged Aleppo will still be at huge risk unless aid groups and the international community can rush food, shelter and medicine to the areas where they are seeking refuge.

The speed of Aleppo’s collapse means there has been little time to prepare for the arrival of huge number of civilians, in areas that are already home to many other refugees, and still under attack from government and Russian planes.

Evacuations of rebel fighters and civilians gathered early pace on Friday, monitors and a rebel official said, with 8,000 people having left since Thursday.

There was no sign, however, of evacuations from two villages besieged by rebels in neighbouring Idlib province, which were expected to be included in the deal.

The new arrivals to rebel areas are likely to be in poor health, weakened by months of siege without proper food or medical care, and are arriving at a time of bitter cold weather.

“It’s winter, it’s freezing, these are tens of thousands of people coming from besieged areas who will need a lot of follow-up treatment because of the rudimentary wartime medical assistance,” said Adham Sahloul, advocacy officer for the Syrian American Medical Society, one of the NGOs working on the ground to aid the new arrivals.

They are also being evacuated to areas that are still war zones, even if they are not being attacked as intensely as east Aleppo. Four hospitals have been bombed out of action in rural Aleppo this year, Sahloul said.

“The problem is that Idlib and the western Aleppo countryside have been constantly targeted themselves by airstrikes, barrel and cluster bombs,” Sahloul said. “So the international community needs to not let its guard down … they need to ensure access to shelter, to aid, to protection.”

The first evacuees left on Thursday. At least 50 medical evacuees headed straight to hospitals, but the others sheltered in a mix of camps and family homes, aid groups said.

Senior Turkish officials said a camp the capacity to host up to 80,000 people would be set up inside Syria two miles from the border. Two sites have been identified, Reuters reported.

The exact number of people waiting for a bus out of east Aleppo is still unclear after the brutal and confusing last stages of the battle for the city, but aid groups agree it is likely to be daunting, even for a country where war has already displaced millions.

“Its certainly quite large,” said Christy Delafield, senior global communications officer for Mercy Corps, a charity that supports nearly 500,000 people across northern Syria each month.

There were up to 250,000 civilians – 100,000 of them children – trapped in east Aleppo when it came under siege. Many of them fled into government-held west Aleppo last week as airstrikes intensified, but there are still thought to be tens of thousands awaiting evacuation.

The Turkish Red Crescent is preparing a camp in Idlib province that could host up to 80,000 people, an official from the group told Reuters. That would exceed an exodus at the start of the year, when aid agencies scrambled to shelter and feed 70,000 people fleeing fighting near Aleppo.

Those people left over the course of several weeks, and Delafield said providing food and shelter was still “very challenging”. The evacuees from the besieged sections of the city could arrive much faster, if enough transport is provided.

The UN also said it was preparing supplies for refugees, and had counselling staff on standby to support children who have endured a long and brutal siege.

“We have been pre-positioning basic supplies, hygiene kits, medicine. Also staff who could do assessment and psychological support,” said Juliette Touma, spokeswoman for Unicef. “That is all going to depend when children come out from Aleppo, but we are on standby.

“What we do know is that there are children, because there are up to 100 trapped in a building. That’s why it’s crucial that an evacuation is happening with dignity and protection,” she said.