Nearly five million Ukrainians have been registered as refugees across Europe since Russia launched its invasion less than four months ago, the United Nations said Thursday.

"The Ukraine war has caused one of the largest human displacement crises in the world," said UNHCR, the UN refugee agency.

An update of the agency’s data portal on the Ukraine situation, aimed to better reflect movements to and from the war-ravaged country, showed that a total of 4,816,923 Ukrainians had been registered as refugees across 44 European countries since February 24.

Far more will have actually left the country, with UNHCR data showing that more than 7.3 million border crossings out of Ukraine had been recorded by June 7.

Another 2.3 million crossings had been registered back into the country, the data showed.

UN officials have said some people have gone back and forth for various reasons, including visiting families, checking their properties, helping others to escape or returning to their jobs.