Two million people — half of them children — have fled Ukraine since Russia’s invasion, according to key U.N. agencies and the International Organization for Migration.

The U.N. High Commissioner for Refugees and UNICEF confirmed the figures as more people headed for the borders. Poland has received more than 1.2 million Ukrainian refugees, the most of any nation.

Civilians in one eastern Ukrainian city were leaving on buses Tuesday amid a 12-hour-long cease-fire in that area after Russia and Ukraine agreed on establishing five safe corridors for people to escape the fighting.

Meanwhile, Russian aircraft continued to bomb cities in eastern and central Ukraine overnight. Shelling pounded suburbs of the capital, Kyiv.

As the war entered its 13th day, food, water, heat and medicine have grown increasingly scarce in multiple cities facing electricity outages.