Families in Ukrainian cities are taking refuge from massive swarms of Russian drones, as Moscow steps up its airborne assault with attacks designed to undermine Ukrainian morale.

A concentrated, nine-minute-long Russian drone attack on Ukraine's second largest city of Kharkiv in the middle of the night killed at least two people and injured 57, including seven children, regional officials said on Wednesday.

The assault continued Moscow’s stepped-up drone and missile attacks, which have been ratcheting up for months with nightly bombardments on regions and cities in Ukraine.