Over 12.7 million people have fled their homes in the past two months, including 7.7 million people displaced internally and more than 5 million who have fled over borders, according to UNHCR.
The United Nations has warned 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.
The UN refugee agency, which initially forecast that up to four million people would flee this year, said on Tuesday 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, adding that the displacements show overburdening expansion and rapidity.
Nearly 5.3 million Ukrainians have already fled Ukraine since Russia launched its full-fledged offensive on February 24, fuelling Europe's fastest-growing refugee crisis since World War II.
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 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."
Moreover, 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 offensive 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.
The UN humanitarian agency 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, adding that so far, donors had provided $980 million, covering 44 percent of the updated appeal.
"Continued international support will be essential to enable humanitarians in Ukraine to reach those whose lives have been upended by the war," Laerke said.