The UN refugee agency, UNHCR, said on Wednesday that 874,026 people have fled Ukraine, more than half of which have fled to Poland, according to its count.

According to the UNHCR, 453,982 Ukrainians have fled to Poland, 116,348 people to Hungry and 79,315 to Moldova. The agency said 69,600 people have fled to other European nations.

The World Health Organization on Wednesday warned of a possible COVID-19 surge in Ukraine and critical oxygen shortages with at least three major oxygen plants in the country closed.

Ukraine is experiencing a critical shortage of oxygen impacting the ability to treat those patients.

WHO Director General Dr. Tedros Ghebreyesus said that just prior to the war, Ukraine was experiencing a surge in COVID-19 cases.

With low testing rates since the start of the conflict, there's likely to be significant undetected transmissions, Ghebreyesus said.

Ghebreyesus warned that with low testing and vaccination rates in Ukraine, the risk of large numbers of people developing severe disease increases.

The WHO said it is seeking ways of accessing oxygen from neighboring countries and ways to deliver it safely, saying there is an urgent need to establish a corridor for humanitarian workers and supplies to reach people in need.

Ghebreyesus said he is deeply concerned about the unfolding humanitarian emergency in Ukraine. The first WHO shipment meant to meet the needs of 1,000 patients in Ukraine will arrive in Poland on Thursday. It contains 6 metric tons of supplies for trauma care and emergency surgery.

The WHO has released $5.2 million from their contingency fund for emergencies and said it will need $45 million for Ukraine for the next 3 months and $12.5 million to support neighboring countries in their care for refugees.

-ABC News' Christine Theodorou

Nearly 2,870 Ukrainian nationalists and army have died and some 3,700 have been injured, according to the Russian Defense Ministry.

According to confirmed data from the Russian Defense ministry, 572 Ukrainian troops have been captured.

Russia said civilians wishing to leave Kyiv in the direction of Vasylkiv won't be stopped by its forces.

"Russian troops are not hindering the exit of the civilian population," Russian Defense Ministry spokesman Igor Konashenkov said.

The Russian Defense Ministry also said civilians can leave the city of Mariupol.

"I would like to emphasize that all civilians wishing to leave Mariupol for safety reasons can exit in the eastern direction via the Mariupol-Shyrokyne motorway," Konashenkov said.

-ABC News' Anastasia Bagaeva

Ukrainian President Volodymyr Zelenskyy on Wednesday praised the United Nations General Assembly for its vote to condemn the Russian invasion and call for the withdrawal of Russian troops.

Zelenskyy called the results of the vote "destructive" for the aggressor, and said it shows "a global anti-Putin coalition has been formed and is functioning."

“I praise the approval by the #UN GA with an unprecedented majority of votes of the resolution with a strong demand to Russia to immediately stop the treacherous attack on. I’m grateful to everyone & every state that voted in favor. You have chosen the right side of history," Zelenskyy said in a tweet.

"The world is with us. The truth is on our side. Victory will be ours!” Zelenskyy said.

U.S. Secretary of State Antony Blinken crossed the border into Ukraine Saturday after meeting with Ukrainian Foreign Minister Dmytro Kuleba at the Korczowa Border Crossing Point.

"The entire world stand with Ukraine," Blinken said, and Kuleba added that he hopes Ukrainians will see this as a "clear manifestation that we have friends who literally stand by us."

Blinken said the sanctions imposed so far against Russia are "producing very, very concrete results" and that the pressure will "grow" until this "war of choice is brought to an end."

When asked directly about helping Kuleba with more firepower, Blinken said, "the support for Ukraine not only has been unprecedented, not only is going to continue, it's going to increase."

Kuleba said Ukraine "appreciates" sanctions that have been announced in the last week, but that more economic and political pressure and "necessary weapons," would "save many lives in Ukraine... many sufferings will be avoided."

Kuleba also said that they are “satisfied" with already arranged supplies of anti-tank weapons and ammunition, but that “it’s no secret” they still want fighter jets and air defense systems.

He also thanked the U.S. for sending stingers, and said they were used on Saturday.

"Just today we shot down three Russian attack aircrafts, which were bombing our cities with the use of stingers but we need -- so to say -- big air defense systems to ensure the safety of our skies. If we lose the skies, there will be much, much more blood on the ground,"Kuleba said.

In response to questions about NATO’s refusal to impose a no-fly zone over Ukraine, Kuleba said it’s a "sign of weakness," but stayed optimistic that they will change their minds.

"The time will come," he said.

-ABC News' Conor Finnegan and Justin Gomez