The United Nations warned Tuesday that more than eight million Ukrainians could flee as refugees this year and doubled its aid appeal for those stuck inside the war-ravaged country.
Nearly 5.3 million Ukrainians have already fled Ukraine since Russia launched its full-fledged invasion on February 24, fuelling Europe's fastest-growing refugee crisis since World War II.
The UN refugee agency, which initially forecast that up to four million people would flee this year, said it would need $1.85 billion to support refugees in neighbouring countries.
UNHCR spokeswoman Shabia Mantoo said it was "anyone's guess as to when we will reach this 8.3-million figure", stressing that "the situation is highly dynamic."
"These displacements are still occurring every day. Every hour we are seeing people continue to flee Ukraine," she told reporters in Geneva.
"This displacement has been on such an expansive scale, and the rapidity of this we haven't seen in recent times."
After just two months of war, the Ukraine conflict appears set to soon produce more refugees than Syria, which after 11 years of civil conflict saw 6.8 million of its nationals register as refugees.
The demographics of Ukraine's refugee population also differ from many other crises.
- Millions stranded -
Women and children account for 90 percent of those who have fled abroad, with men aged 18 to 60 eligible for military call-up unable to leave.
The UNHCR said that neighbouring host countries had the capacity to respond to the crisis, but that "the scale of refugee arrivals and the breadth of their needs requires further support for national social protection systems and services."
Nearly six out of 10 Ukrainian refugees -- more than 2.9 million -- have fled to Poland.
While the rapidly rising refugee numbers are staggering, they do not paint the full picture.
Around 7.7 million people have been displaced from their homes but remain inside Ukraine, meaning that 12.7 million total have been uprooted since the invasion began.
"Almost 13 million more people are also estimated to be stranded in affected areas or unable to leave due to security risks," Mantoo said.
The UN humanitarian agency OCHA estimated Tuesday that 15.7 million people in Ukraine are in need of humanitarian aid, up from its previous estimate of 12 million.
Before the invasion, Ukraine had a population of 37 million in the regions under government control, excluding Russia-annexed Crimea and the pro-Russian separatist-controlled regions in the east.
The UN humanitarian agency has more than doubled its estimate for how much money is needed to assist people inside the war-torn country.
It had a flash appeal on March 1, calling for $1.1 billion to help some six million people inside the country over three months.
On Tuesday, OCHA said it now estimated that more than $2.25 billion was necessary to address the escalating needs inside Ukraine, and said the appeal was meant to cover assistance through August.
The revised appeal aims to help 8.7 million in most dire need of assistance, OCHA spokesman Jens Laerke told reporters.
He said that so far, donors had provided $980 million, covering 44 percent of the updated appeal.
Those funds, he said, have "enabled the UN and our partners to reach 3.4 million people inside Ukraine with some kind of humanitarian assistance."
"Continued international support will be essential to enable humanitarians in Ukraine to reach those whose lives have been upended by the war."