More than eight million Ukrainians could flee as refugees this year, and the United Nations said it doubled its aid appeal for those stuck in 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 originally predicted 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, despite the fact that the situation is highly dynamic. "Every hour we are seeing people flee Ukraine," she told reporters in Geneva.
This displacement has been on an expansive scale, and we haven't seen in recent times. After just two months of war, Ukraine seems to have more refugees than Syria, which has seen 6.8 million of its nationals register as refugees after 11 years of civil conflict.
The demographics of Ukraine's refugee population are different from many other crises.
The 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.
The rapid rise of refugee numbers is staggering, but they do not paint the full picture.
Around 7.7 million people have been displaced from their homes but remain in Ukraine, meaning that 12.7 million people have been uprooted since the invasion began.
Nearly 13 million more people are estimated to be stranded in affected areas or unable to leave due to security risks, Mantoo said.
The UN humanitarian agency OCHA estimated that 15.7 million people in Ukraine need 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 help people in the war-torn country.
It had a flash appeal on March 1, calling for $1.1 billion to help six million people in the country over three months.
On Tuesday, OCHA estimated that more than $2.25 billion is needed to address the escalating needs in 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 donors had provided $980 million, covering 44 percent of the updated appeal.
He said that funds have allowed the UN and our partners to reach 3.4 million people in Ukraine with humanitarian assistance. There is a need for continued international support to allow humanitarians in Ukraine to reach those whose lives have been upended by the war.