Fears of a growing refugee crisis in Europe loom amid Russia’s attack on Ukraine

The Russian invasion of Ukraine is forcing many Ukrainians to leave their homes to seek shelter, with long lines already forming at the border and the potential for severe humanitarian consequences looming.

More than 50,000 Ukrainians left the country within less than 48 hours, United Nations High Commissioner for Refugees Filippo Grandi said on Friday. The majority have fled to Poland and Moldova, he said.

The U.N. refugee agency estimates that some 100,000 Ukrainians have already been forced from their homes, UNHCR spokesperson Shabia Mantoo told ABC News, cautioning that the agency does not have exact numbers.

“But there clearly has been significant displacement inside the country and some movements towards and across the borders,” she said.

In a statement, Grandi said the consequences for this invasion will be devastating.

"The humanitarian consequences on civilian populations will be devastating. There are no winners in war, but countless lives will be torn apart," Grandi said.

USAID also activated a disaster assistance response team to Poland "to respond to growing humanitarian needs stemming from Russia's unprovoked and unjustified further invasion of Ukraine," the agency announced. The agency said it will coordinate U.S. disaster response to the potential refugee crisis and the humanitarian needs in Ukraine.

Experts say the longer the conflict carries on, the greater the crisis could become.

The crisis is likely to start out as an internal displacement of people, as Russian troops continue to make advances into Ukraine, Serena Parekh, a professor of philosophy at Northeastern University and a researcher who focuses on the displacement of refugees, told ABC News.

"That refers to the people who have just left their homes gotten in their car, they're driving somewhere anywhere, just to get out of the conflict," Parekh said. "That's going to be the first crisis."

The ability of international organizations to continue working in Ukraine, or whether they themselves will become targets, will also play a role in the internal crisis, experts say.

Attacks on non-military locations happened in Ukraine in 2014 when Russia annexed Crimea, leaving 1.4 million people in internal displacement, Daniel Balson, an advocacy director at Amnesty International, told ABC News.

Balson said Amnesty International has recorded three attacks in Ukraine involving the usage of explosive weapons with wide area affects in densely populated areas, including a hospital (which is protected under international law) and a residential block.

"This is becoming part of a pattern. And that pattern demonstrates a blatant disregard for the lives of civilians by using these indiscriminate weapons and heavily densely populated areas," Balson said.

"Ukraine has about 40 million people in there. I mean, we're talking about very large numbers of people who are impacted and affected," he said.

Parekh said if the conflict continues, the crisis could likely move out of Ukraine and into neighboring countries.

"Secondarily, people will start crossing borders into Eastern Europe, in particular Poland. And the rate and the exact numbers remain to be seen," Parekh said.

Neighboring countries are bracing for an influx of Ukrainians fleeing the conflict.

"Poland has said they're prepared to take upwards of a million refugees, which is great, in some sense, because the change in attitude towards Ukrainian refugees as compared to the Syrian refugees that were coming into Bella Luce last year, is very, very striking," Parekh said.

"It's not clear that they actually have the capacity to take that many refugees," she said. "In 2021, they only took in 5,000 Refugees in total. So it's a huge leap from that to say that they are preparing to take in a million refugees."

Parekh said that countries that share a border with Ukraine, including Poland, Hungry and Romania, will likely need a lot of support from the international community in order to be able to accommodate what could be hundreds of thousands of people crossing their borders.

The problem with supporting refugees is not one of "technical capacity," Balson said.

"It's often a problem with political will. When a government decides what it will concentrate its resources on, it's imperative that supporting refugees be at the top of that list. Has this always been the case in the past? No," Balson said.

He said the international community has shown some positive signs, with border countries like Poland saying they will keep their borders open.

Parekh said it is likely there will be a lot of sympathy toward Ukrainian refugees for several reasons including the fact that they are fleeing a common enemy and the fact that Ukrainians are white, largely Christian and seen as Europeans.

"There's racism that prevents all people from being treated equally, but there's also a sense in which humans seem to have a natural tendency to be sympathetic to people they perceive to be like them in some significant way," Parekh said.

The international community has tended to downplay the risk of refugee crises stemming from previous conflicts until it was unavoidable, but that does not seem to be the case with Ukraine, Parekh said.

"The language that people are using to talk about the Ukrainian crisis right now is great and it shows a readiness and a willingness to acknowledge the strong likelihood that this war will produce substantial refugee crisis," Parekh said.