People wait to board buses during their evacuation in Kramatorsk, Ukraine, Saturday, April 9, 2022. AP
The UNHCR said there were 4,441,663 Ukrainian refugees on Saturday.
That was 59,347 more than the previous day.
Europe has not seen such a flood of refugees since World War II.
Ninety percent of those who have fled Ukraine are women and children, as the Ukrainian authorities do not allow men of military age to leave.
According to the UN's International Organization for Migration (IOM), around 210,000 non-Ukrainians have also fled the country, sometimes encountering difficulties returning to their home countries.
The United Nations estimates that 7.1 million people have been displaced within the country, according to figures published by the IOM on April 5.
More than 11 million people, or more than a quarter of the population, have been forced to flee their homes, cross the border into neighbouring countries or seek refuge elsewhere in Ukraine.
Before the conflict, Ukraine was home to more than 37 million people in territory controlled by Kyiv -- which does not include Crimea, annexed by Russia in 2014, or areas in the east under the control of pro-Russian separatists.
Poland hosts by far the largest number of refugees.
Since February 24, 2,564,994 have entered Poland, according to the UNHCR.
Many of them then travel to other European countries.
Of those who remain in Poland, 700,000 have already been granted a national identification number, the UNHCR said Friday.
The number is widely used in dealings with Polish public institutions, health services, telephone numbers and access to certain banking services.
Polish border police estimate that more than 500,000 people have returned to Ukraine since the conflict.
Poland had around 1.5 million Ukrainian immigrant workers before the war.
According to the UN refugee agency, 678,081 people had travelled to Romania as of April 8, most of whom arrived via Moldova and then continued on to other countries.
After a visit to Romania this week, Raouf Mazou, the UNHCR's assistant high commissioner for operations, acknowledged "the rapid action taken by the Romanian government to ensure access to rights and services through temporary protection".
According to the UNHCR, 406,611 Ukrainians have entered Moldova, a small country of 2.6 million people that is among the poorest in Europe but also the closest to the Ukrainian port of Odessa.
The European Commission is encouraging Ukrainian refugees to continue their journey to settle in a European Union country more able to bear the financial burden.
As of April 8, Hungary had taken in 413,888 Ukrainians, according to the UNHCR.
As of April 8, a total of 310,989 people had arrived from Ukraine since the start of the war, according to the UNHCR.
The number of refugees in Russia stood at 389,845 as of April 8.
Between February 21 and 23, 113,000 people crossed into Russia from the separatist regions of Donetsk and Lugansk in eastern Ukraine.
As of April 7, Belarus had taken in 19,096 people.
The UNHCR said that for the countries bordering Ukraine that are part of the Schengen zone (Hungary, Poland and Slovakia), the figures presented by the High Commissioner count those who have crossed the border and entered the country.
"UNHCR believes that a large number of people have continued their journey to other countries."
It also said it did not count people from neighbouring countries who were leaving Ukraine to return home.