The number of refugees fleeing the war in Ukraine is expected to top 2 million in the next two days, the head of the United Nations High Commissioner for Refugees (UNHCR) said Tuesday, making it Europe's "fastest growing refugee crisis" since World War II.

Refugees from Ukraine rest at a temporary shelter in the main train station of Krakow on March 6, 2022, as they wait to be relocated to other temporary accommodations in Poland or abroad.

A woman looks after her child at a refugee shelter after Russia's invasion of Ukraine, in Beregsurany, Hungary, March 7, 2022.

A woman and a man use their phones to communicate through a train window as passengers, including people fleeing Russia's invasion of Ukraine, board a train to leave the city of Odessa, Ukraine, March 6, 2022.

A woman fleeing the Russian invasion of Ukraine takes a rest after crossing the border from Ukraine to Poland, at the border checkpoint in Medyka, Poland, March 6, 2022.

A woman rests at a refugee shelter after fleeing Russia's invasion of Ukraine, in Beregsurany, Hungary, March 7, 2022.

A child eats a cookie as she stands in a temporary accommodation for refugees at the train station, after fleeing the Russian invasion of Ukraine, in Przemysl, Poland, March 7, 2022.

A family walks after fleeing from Ukraine to Romania, following Russia's invasion of Ukraine, at the border crossing in Siret, Romania, March 7, 2022.

A girl waits outside a temporary accommodation and transport hub for refugees at a former shopping mall, after fleeing the Russian invasion of Ukraine, in Przemysl, Poland, March 7, 2022.

People arrive by ferry after fleeing from Russia's invasion of Ukraine, at the Isaccea-Orlivka border crossing, Romania, March 7, 2022.

A woman sits inside a bus after fleeing from Ukraine to Russia during the Ukraine-Russia conflict, at the Veselo-Voznesenka border crossing in the Rostov region, Russia, March 7, 2022.

People arrive at the Veselo-Voznesenka border crossing after fleeing from Ukraine to Russia during the Ukraine-Russia conflict, in the Rostov region, Russia, March 7, 2022.

A woman from Ukraine reacts as she receives a hug from a volunteer after arriving at Berlin's central station, following Russia's invasion of Ukraine, in Berlin, Germany, March 7, 2022.

Refugees evacuated on a train from Kyiv, following the Russian invasion of Ukraine, wait for transfer to Poland outside the train station in Lviv, Ukraine, March 7, 2022.

An abandoned stroller is pictured on a street next to the border crossing from Ukraine to Poland, where people fleeing the Russian invasion of Ukraine at the border checkpoint in Medyka, Poland, March 7, 2022.

Rita and her daughter Vika, refugees fleeing from Kyiv, arrive on a train from Przemysl at Berlin's central station, following Russia's invasion of Ukraine, in Berlin, Germany, March 7, 2022.

A train with refugees fleeing Ukraine crosses the border in Medyka, Poland, March 7, 2022.

People fleeing the Russian invasion of Ukraine eat next to a bonfire after crossing the border from Ukraine to Poland, at the border checkpoint in Medyka, Poland, March 7, 2022.

Refugees evacuated on a train from Kyiv, following the Russian invasion of Ukraine, arrive at the train station in Lviv, Ukraine, March 7, 2022.

A child wrapped in a thermal blanket to keep warm boards a bus after fleeing from Ukraine and arriving at the border crossing in Medyka, Poland, March 7, 2022.

Volunteers prepare food for people fleeing the Russian invasion of Ukraine at the border checkpoint in Medyka, Poland, March 6, 2022.

Volunteers sort piles of donated clothes under a shiny disco ball inside a ballroom converted into a makeshift refugee shelter at a 4-star hotel & spa, in Suceava, Romania, March 4, 2022.

A Ukrainian police officer runs while holding a child as the artillery echoes nearby, while fleeing Irpin on the outskirts of Kyiv, Ukraine, March 7, 2022.

Ukrainian soldiers and militiamen carry a woman in a wheelchair as the artillery echoes nearby, while people flee Irpin on the outskirts of Kyiv, Ukraine, March 7, 2022.

A firefighter holds the baby of a refugee fleeing the conflict from neighboring Ukraine at the Romanian-Ukrainian border, in Siret, Romania, March 7, 2022.

A Ukrainian refugee with a dog waits at the Ukrainian refugees distribution center in Korczowa, Poland, March 5, 2022.

A refugee from Ukraine carries a parrot in a cage upon arrival in Przemysl, Poland, March 4, 2022.

A woman sits in a Temporary Reception Center in Korczowa, March 2, 2022.

Refugees from Ukraine rest at a temporary shelter in the main train station of Krakow, March 6, 2022, as they wait to be relocated to other temporary accommodations in Poland or abroad.

A young refugee coming from Ukraine sits on a woman's lap inside a bus after arriving at the North Railway Station in Bucharest, early March 4, 2022.

A child sleeps in the train station in Przemysl, Poland, March 7, 2022, from where Ukrainian refugees are relocated by train across Poland.

Refugees from Ukraine queue for a bus to further destinations at the distribution center in Korczowa, Poland, March 5, 2022.

Ukrainian refugees queue to file for residency permits at the regional assistance center for refugees in the Prague's Congress Centre in Prague, Czech Republic, March 7, 2022.

Police manage people as they wait to board a bus, at a temporary accommodation center, after fleeing the Russian invasion of Ukraine, in Korczowa, Poland, March 6, 2022.

Clowns play with the children of Ukrainian refugees in the regional assistance center at the Prague Congress Center on March 7, 2022, in Prague, Czech Republic.

Refugees charge their mobile devices as they wait for transfer after fleeing the ongoing Russian invasion at the main train station in Lviv, Ukraine, March 5, 2022.

Ukrainian refugees are seen at the temporary refugee center in a local primary school at Tiszabecs, eastern Hungary, Feb. 28, 2022.

A woman fleeing the Russian invasion of Ukraine holds a cup of tea as she takes shelter inside a tent after crossing the border from Ukraine to Poland, at the border checkpoint in Medyka, Poland, March 6, 2022.

Ukrainian refugees look from a window in the regional assistance center at the Prague Congress Center on March 7, 2022, in Prague, Czech Republic.

A woman cries as she comforts her son after learning she has to leave a bus that was reserved for the evacuation of orphans fleeing the ongoing Russian invasion outside the main train station in Lviv, Ukraine, March 5, 2022.