Since Russia invaded Ukraine last week, an estimated 660,000 refugees have fled to other countries -- with the number only expected to grow.
The UNHCR said in a statement Tuesday the conflict could lead to "Europe's largest refugee crisis this century" as displaced people pour into Poland, Romania, Slovakia, Hungary and Moldova.
Non-profit organizations and other groups are warning many could wind up lacking access to basic health and medical needs including food, clean water, shelter, hygiene supplies and medication. And they say cases of communicable diseases, such as COVID-19 and polio, have the potential to grow along with gastrointestinal ailments.
That's on top of trekking, on foot in cases, in the middle of winter in Eastern Europe.
"Fleeing your home is a last act of desperation," Chris Skopec, executive vice-president of global health at Project Hope, a humanitarian nonprofit organization providing assistance to Ukrainian refugees, told ABC News. "All of your support networks are within your immediate community and, once you leave that, you excessively become more vulnerable to all kinds of things."
Refugees may not have access to food, water or sanitation
Humanitarian groups say there are many health concerns for refugees fleeing the crisis in Ukraine.
Although there are public transit buses, trains and taxis that have been taking people to border checkpoints, some refugees have had to reach checkpoints on foot.
Additionally, stories have circulated Ukrainians waiting up to 60 hours at border crossings just to get into a neighboring country, Skopec said.
"If you have less than sanitary conditions, if you're walking on the road for days or sitting in your car, you don't have access maybe to clean drinking water or the ability to wash or access proper hygiene facilities," he said. "Then you've got concerns about gastrointestinal diseases, which can lead to other health conditions and really overall weaken the body."
Refugees could also fall ill as they wait in long lines at the border in freezing temperatures. Temperatures usually don't go much higher than 38 degrees Fahrenheit and fall to the low 20s at night.
"We're talking about winter in central Europe," Dr. Andrea Barschdorf-Hager, CEO of Care Austria, a nonprofit also helping Ukrainian refugees, told ABC News. "The weather conditions are hard and people are literally fleeing with just one winter jacket."
When Russia invaded, Ukraine was already dealing with two public health crises, the first linked to the COVID pandemic.
Even while daily average COVID cases peaked at 37,000 last month, as data from Johns Hopkins University shows, less than 40% of Ukrainians aged 60 and older have received at least one COVID-19 vaccine dose, according to the World Health Organization.
The country has also been trying to beat back a polio outbreak since October 2021 due to low immunization rates. During that time frame, at least one child was identified with paralytic polio and 19 other children have been infected, but not paralyzed, according to the United Nations Children's Fund.
People traveling in large groups without masks or social distancing, drinking contaminated water or coming in contact with an infected person could lead to surges of these diseases in the refugee population.
"When you have a large population in mass movement fleeing the country, you don't have the kind of personal protective equipment required to prevent the spread of infections," Skopec said.
Right now, there are no reports that COVID-19 is spreading among the refugee population.
'Stress and anxiety' for those fleeing their homes
There are mental health concerns for refugees as well.
Skopec said one of the concerns is for those with chronic mental health conditions, who will be traveling without access to care or their medications. The other concern is broader and affects all those who are stressed due to fleeing.
"Everybody doing this is going through a tremendous amount of stress and anxiety," Skopec said.
Barschdorf-Hagersaid said it will be important to provide psychosocial support to refugees when they cross the border.
"Not everyone is traumatized, but they have to digest what has happened," she said. "We need to set up social workers for people who want to talk to a social worker. The refugees need help to integrate and some moments will haunt them for the rest of their lives.
She continued, "We are in a war situation and we have to make them feel welcome and let them know they have a safe space to stay, come and go."
Refugees need to be met with care packages and hygiene kits
Skopec said Project Hope is currently deploying four different teams to Poland, Moldova, Romania and Ukraine, and focusing on the medical and health needs of refugees, including those who have not crossed into neighboring countries.
"So in Poland, we are simultaneously looking to get medical supplies into Ukraine to distribute to medical facilities while at the same time offering support to the Polish health authorities in terms of receiving refugees and making sure that they've got proper screening and proper basic care available for them," he said.
Skopec added the organization has also put together interagency emergency kits, which are described by the WHO as being filled with medicines such as ibuprofen and morphine and medications to treat conditions including cardiovascular diseases, diabetes and pulmonary diseases.
Each kit can treat 30,000 people for one month and Project Hope has seven kits on standby whenever governments request them.
Meanwhile, Barschdorf-Hagersaid said CARE Austria is working with its partner organization, People in Need, to supply care packages of clean water and food, including baby food, to refugees as well as hygiene kits.
"I don't know of any border where there are enough sanitation places. There are not enough toilets, not enough washing stalls," she said. "So the kits include diapers for babies, sanitary pads for young girls and women and so on."
Barschdorf-Hagersaid also said the refugees need cash assistance so they can buy tickets to get their families living elsewhere in Europe or so they can buy things.
"Cash assistance is important to meet the needs of the moment because banks are not functioning in Ukraine," she said. "It's really key that people get cash assistance."