More than 5 million refugees have fled Ukraine since Russia launched its unprovoked invasion, according to United Nations refugee agency data on Wednesday.

State of play: The U.N. refugee agency has labeled the exodus the fastest-growing refugee crisis in Europe since World War II.

• “The speed of the displacement, coupled with the huge numbers of people affected, is unprecedented in Europe in recent memory,” said U.N. High Commissioner for Refugees Filippo Grandi during his first visit to Ukraine since the invasion began.
• “I have spoken with women, with children, who have been gravely affected by this war,” he added.
• “Forced to flee extraordinary levels of violence, they have left behind their homes and often their families, leaving them shocked and traumatized. The protection and humanitarian needs are enormous, and continue to grow. And while critically urgent, humanitarian aid alone cannot give them what they really need – and that is peace.”

Driving the news: Most Ukrainian refugees have crossed into Poland, and others have gone to Romania, Hungary, Moldova, Slovakia and other European countries. Many have also fled to Russia.

• "People are under stress ... and when people are scared they become egoist and forget about everything," Natalia Pivniuk, a Ukrainian woman from Lviv, told AP earlier this month.
• She said people were pushing to get on a train to flee. It was "very scary, and dangerous physically and dangerous mentally."

Zoom in: Nearly two-thirds of all Ukrainian children have been displaced from their homes due to the war, UNICEF said this week.

• "They have been forced to leave everything behind: Their homes, their schools, and often, their family members," UNICEF emergency programs director Manual Fontaine said.
• "Every day the war continues, children will continue to suffer," he said.
• More than 90% of the more than 4.7 million Ukrainians who fled the country are women and children, Fontaine said.

The big picture: UN aid agencies have warned that fuel, cash and medical supplies were dwindling in Ukraine.

• Ukraine's water system is also "at risk of complete collapse," the United Nations warned last week.
• UNICEF said 1.4 million people in Ukraine no longer have access to piped water and 4.6 million people are at risk of losing their water supply.
• "The picture is grim and could get worse still," UN emergency relief coordinator Martin Griffiths told the Security Council earlier this month.
• "The elderly and people with disabilities find themselves trapped and unable to flee," he added.
• "Children will miss school and face a great risk of physical harm displacement and unimaginably severe emotional stress. Women, so often disproportionately affected by conflict ... will be at even greater risk of gender-based violence."

Go deeper:

• Axios explains Ukraine
• The latest on the Russia-Ukraine crisis

Editor's note: This post has been updated with new estimates on the number of refugees.