More than 4.2 million Ukrainian refugees have now fled the country since the Russian invasion, the United Nations said Monday, adding that the humanitarian situation was worsening.

UNHCR, the UN refugee agency, said 4,215,047 Ukrainians had fled the country since the war began on February 24 -- a figure up 38,646 on the numbers for Sunday. 

"The humanitarian needs are growing by the minute as more people flee the war in Ukraine," the UN's International Organization for Migration said.

The IOM says that in addition to Ukrainian refugees, nearly 205,500 non-Ukrainians living, studying or working in the country have also left. 

Meanwhile, nearly 6.48 million people were estimated to be internally displaced within Ukraine as of mid-March, according IOM.

Before the Russian invasion, Ukraine had a population of 37 million in the regions under government control, excluding Russia-annexed Crimea and the pro-Russian separatist regions in the east. 

Women and children account for 90 percent of those who have left Ukraine, with men aged 18 to 60 eligible for military call-up and unable to leave.

The UN children's agency UNICEF said in late March that more than half of the country's estimated 7.5 million children had been displaced -- 2.5 million internally and two million abroad.

Here is a breakdown of how many Ukrainian refugees have fled to neighbouring countries, according to UNHCR:

- Poland -

Nearly six out of 10 Ukrainian refugees -- 2,451,342 so far -- have crossed into Poland, according to the UN tally. 

Many people who go to Ukraine's immediate western neighbours travel on to other states in Europe's Schengen open-borders zone.

But Poland's deputy interior minister said 1.5 million have remained in the country, of whom 600,000 have already obtained a Polish national identification number, used for accessing services.

Alexander Mundt, UNHCR's senior emergency coordinator in Poland, said that as people crossed the border at Medyka, he wanted to make sure they had information as to what they could expect and how they could keep safe.

"All assistance is free, and here on this side of the border the response by the Polish civil society and volunteers in every town has been staggering. I've never seen anything like it," he said.

- Romania -

A total of 643,058 Ukrainians have entered the EU member state, including a large number who crossed over from Moldova, wedged between Romania and Ukraine. 

The vast majority are thought to have gone on to other countries. 

- Moldova -

The Moldovan border is the closest to the major port city of Odessa, which was hit by air strikes on Sunday. Some 394,740 Ukrainians have crossed into the non-EU state, one of the poorest in Europe.

Most of those who have entered the former Soviet republic of 2.6 million people have moved on.

But around 93,000 have stayed, with the UN Development Programme saying that some 80 percent are being housed by private individuals.

- Hungary -

A total of 390,302 Ukrainians have entered Hungary. 

- Russia -

Some 350,632 refugees had sought shelter in Russia as of last Tuesday.

In addition, 113,000 people crossed into Russia from the separatist-held pro-Russian regions of Donetsk and Lugansk in eastern Ukraine between February 21 and 23. 

- Slovakia -

A total of 301,405 people have crossed Ukraine's shortest border into Slovakia. 

- Belarus -

Another 15,281 refugees had made it north to Russia's close ally Belarus.