WARSAW, Poland (AP) — Warsaw's mayor is appealing for international help as the city becomes overwhelmed by refugees, with more than a tenth of all those fleeing the war in Ukraine arriving in the Polish capital.

Some seek to wait out the war or settle in the city, while others merely use Warsaw as a transit point to head further west, turning the city's train stations into crowded hubs where people are camping out on floors.

“We are dealing with the greatest migration crisis in the history of Europe since World War II. ... The situation is getting more and more difficult every day,” Mayor Rafal Trzaskowski said, adding that “the greatest challenge is still ahead of us.”

To be sure, the welcome Warsaw has given Ukrainians as the nation struggles to resist Russia's invasion is wholehearted. Across the city, people have mobilized to help by collecting donations and volunteering at reception centers. City monuments and buses fly Ukraine’s blue-and-yellow flag to show solidarity with the neighboring nation.

But the challenge is enormous. Much of the burden so far is being carried by volunteers taking time off work, a situation not sustainable in the long run.

Trzaskowski noted on Friday that psychologists, giving just one example, had been volunteering to help refugees but soon will need to return to their jobs.

The decline in the city's ability to absorb a massive number of new arrivals comes as the people fleeing war are those who have witnessed greater trauma than those who arrived earlier.

“At the beginning the people who came here were running away in panic from the war they saw in the media and that they heard about. Now we find there are people escaping from bombs," said Dorota Zawadzka, a child psychologist volunteering at a center for refugees set up in the Torwar sports center.

"This is a completely different kind of refugee. They are afraid of everything. They sit in their jackets. Children are scared, they don’t want to play, their mothers have such empty eyes.”

The war has already forced 2.5 million people to flee, according to the International Organization for Migration on Friday, and more than half of those go to Poland. As of Friday more than 1.5 million refugees had entered Poland, according to Poland’s Border Guard agency.

Trzaskowski said Friday that 300,000 refugees have arrived in the capital since the war began on Feb. 24.

Poland’s train stations have become major transfer points for Ukrainians who fled the war, with people arriving and transferring to trains to points further west.

This week the central station was filled with people, some in a state of limbo as they awaited their next move, with people sleeping on the floors of the station, others reading on their phones, petting cats and dogs or playing with children.

Volunteers moved about, bringing snacks to people and helping them to sort through used clothes.

Some handed out books to children in an attempt to cheer up the youngest of those whose lives had been turned upside down by Russia’s invasion.

Train after train pulled into the station carrying people who had crossed from Ukraine into Poland, while trains to Vienna and other destinations carried them onward.