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 six people and injured 64, including nine children, Ukrainian officials said on Wednesday.

The attack used almost 500 drones and missiles, breaking a record set just days earlier, as Russia tries to overwhelm Ukraine’s air defenses, which shot down most of the weapons.