Three weeks into Russia’s war, more than 2.8 million people have fled Ukraine and 6.7 million people have been internally displayed, UN agencies said on Monday.
According to the UN's refugee agency UNHCR, over 1.7 million people crossed into Poland to run away from the war in Ukraine.
Hungary has received over 255,000 people, while over 100,000 people have entered Slovakia and Moldova each.
Some 131,000 people have fled to Russia and nearly 85,000 others have gone to Romania.
"The current estimated number of people impacted in Ukraine is 18 million, of which 6.7 million are internally displaced," the World Health Organization said.
Medical supplies have been severely disrupted, said the WHO, with many distributors not operational and some stockpiles inaccessible due to military operations.
Medicine supplies running low
"Medicine supplies are running low, and hospitals are struggling to provide care to the sick and wounded," said the UN health agency.
"Since Russia's military offensive began in Ukraine on 24 February, WHO has worked around the clock to ensure a constant flow of health supplies, so that neighboring countries have the infrastructure and expertise to meet urgent needs of refugees," it added.
The WHO said it is also seeking to support Ukraine's health system to meet people's immediate health needs within its borders.
The world health body said it is shipping medical supplies to Ukraine.
Included are oxygen generators, generators to maintain electrical supply in affected health facilities, defibrillators, monitors, anesthesia drugs, rehydration salts, gauze, and bandages.
On Sunday, the International Committee of the Red Cross warned that a "worst-case scenario" awaits hundreds of thousands of civilians trapped in Ukraine's port city of Mariupol facing starvation or death unless a concrete humanitarian agreement is reached urgently.
"Hundreds of thousands of the city's residents are now facing extreme or total shortages of basic necessities like food, water, and medicine," said a statement by the ICRC.
Ukrainian President Volodymyr Zelenskyy said over the weekend that the Russian army had suffered unprecedented losses in Ukraine and its biggest blow in decades.
Zelenskyy spoke at a virtual news conference Saturday from the presidential office in Kyiv while answering a question about talks between Ukraine and Russia.
Evaluating the possibility of the Russian army entering the capital, he said: "If they decide to carpet bomb (Kyiv) and simply erase the history of this region, the history of the Kyivan Rus, the history of Europe, and destroy all of us, then they will enter Kyiv."
The Kyivan Rus was a loose federation in Eastern and Northern Europe from the late 9th to the mid-13th century.