The mayors of both Warsaw, the capital, and Krakow, Poland’s second largest city, said that they are struggling to accommodate the sheer number of people who are arriving — and urged the United Nations and European Union to intervene.

More than 2.5 million Ukrainians have fled to neighboring countries since the war started on Feb. 24, according to the United Nations High Commissioner for Refugees. The vast majority — 1.5 million people — have sought refuge in Poland, with smaller numbers fleeing to other countries such as Hungary, Moldova and Slovakia.

More than 2 million people have left Ukraine, foreshadowing a massive humanitarian crisis

The head of UNHCR, Filippo Grandi, said the Ukraine exodus was “the fastest-growing refugee crisis in Europe since World War II.”