More than 4.5 million people have been forced to flee Ukraine since Russian forces invaded on Feb. 24, according to the latest figures from the United Nations Refugee Agency.

The tally from the U.N. High Commissioner for Refugees (UNHCR) amounts to just over 10% of Ukraine's population -- which the World Bank counted at 44 million at the end of 2020 -- on the move across borders in 47 days.

More than half of the refugees crossed into neighboring Poland, UNHCR figures show.

"The escalation of conflict in Ukraine has caused civilian casualties and destruction of civilian infrastructure, forcing people to flee their homes seeking safety, protection and assistance," the UNHCR said in a statement alongside the data updated Sunday.

"In the first five weeks, more than four million refugees from Ukraine crossed borders into neighbouring countries, and many more have been forced to move inside the country," the agency noted. "In light of the emergency and the scale of humanitarian needs of refugees from Ukraine, an inter-agency regional refugee response is being carried out, in support of the efforts of refugee-hosting countries."

Russia's invasion is expected to shrink Ukraine's economy by about 45.1% this year, the World Bank said on Monday.

"Ukraine needs massive financial support immediately," said Anna Bjerde, World Bank vice president for the Europe and Central Asia region.

The World Bank said a $3 billion package is being prepared for Ukraine. Already $925 million in emergency funding has been mobilized for Ukraine to help pay wages for hospital workers, pensions for the elderly and social programs for the vulnerable. The Bank Group is also looking at how to support refugees in host countries.

Meanwhile, Russia, hit by unprecedented sanctions, has already plunged into a deep recession with output projected to contract by 11.2% in 2022, the World Bank said.

-ABC News' Christine Theodorou

Nine humanitarian corridors are expected to open in eastern Ukraine on Monday to allow civilians escape heavy fighting, according to Ukrainian Deputy Prime Minister Iryna Vereshchuk.

She said in a statement via social media Monday that evacuation routes were agreed upon for those traveling by private cars from besieged Mariupol in the Donetsk Oblast, as well as from Berdyansk, Tokmak and Enerhodar in the Zaporizhzhia Oblast -- all of which lead to the southeastern city of Zaporizhzhia. Buses from Zaporizhzhia city were also waiting to pass a checkpoint in Vasylivka, according to Vereshchuk.

In the Luhansk Oblast, Vereshchuk said routes were established from the cities of Severodonetsk, Lysychansk, Popasna, Hirske and Rubizhne, leading to the city of Bakhmut in the Donetsk Oblast.

The United Kingdom is warning of Russia's possible use of phosphorus munitions in the besieged Ukrainian city of Mariupol.

Russian forces have already been accused of using phosphorus bombs in Ukraine since launching an invasion on Feb. 24. When deployed as a weapon, phosphorus can inflict excruciating burns and lead to infection, shock and organ failure.

After withdrawing troops from the north, the Russian military is said to be refocusing its offensive on the Donetsk and Luhansk oblasts in eastern Ukraine's disputed Donbas region, where Russia-backed separatist forces have been battling Ukrainian soldiers since 2014. Mariupol, in the Donetsk Oblast, and its residents have been under heavy Russian bombardment for over a month, but Moscow has so far failed to win full control of the strategic port.

"Russian forces prior use of phosphorous munitions in the Donetsk Oblast raises the possibility of their future employment in Mariupol as fighting for the city intensifies," the U.K. Ministry of Defense said Monday in an intelligence update.

Meanwhile, Russian shelling has persisted in the Donetsk and Luhansk oblasts, according to the ministry, "with Ukrainian forces repulsing several assaults resulting in the destruction of Russian tanks, vehicles, and artillery equipment."

"Russia's continued reliance on unguided bombs decreases their ability to discriminate when targeting and conducting strikes while greatly increasing the risk of further civilian casualties," the ministry added.

President Joe Biden on Thursday announced a new $800 million security assistance package to help Ukrainians fighting in the eastern Donbas region. This funding includes heavy artillery weapons, tactical drones and howitzers.

This package includes 72 new howitzers. Combined with the 18 howitzers announced last week, the 90 howitzers headed to Ukraine can equip five battalions, according to the administration.

Biden noted that he’s run out of pre-approved money and equipment to send to Ukraine and he appealed to Congress to approve more.

When pressed by ABC News on how long the U.S. can sustain this level of spending, Biden said, “We have the capacity to do this for a long time."

He went on, "The question is, are we going to continue to maintain the support of the international community? And keep the pressure on Putin to prevent him from overrunning the country, No. 1, and No. 2, make sure we continue to maintain the economic sanctions, which, over time, and we're beginning to see, they’re devastating their economy and their ability to move forward."

Biden also announced a separate $500 million in economic aid to Ukraine to help fund government operations like salaries, pensions and social programs.

The president added that the U.S. is now banning Russian-affiliated ships from American ports.

Biden met with Ukrainian Prime Minister Denys Shmyhal Thursday morning ahead of his remarks.

-ABC News' Luis Martinez and Sarah Kolinovsky