The United Nations Children's Fund, or UNICEF, says children in Ukraine have been forced to spend up to 5,000 hours sheltering underground since the start of the Russian invasion.

UNICEF reports that nearly 6,200 air raid alerts have been issued since February 2022 in the eastern region of Donetsk, and around 3,500 in Kharkiv and in the southern region of Zaporizhzhia.

It said that children in Ukraine's frontline areas have been forced to spend between 3,000 and 5,000 hours, which is equivalent to between four and seven months, sheltering in basements and underground subway stations.

The UNICEF warned of the serious psychological impacts of war upon children.

The agency said half of those aged 13 to 15 have trouble sleeping, and one in five suffer intrusive thoughts and flashbacks, which are typical manifestations of post-traumatic stress disorder.

It also said 40 percent of Ukraine's children cannot access continuous education due to a lack of facilities, adding that half of school-age children in areas nearer to the frontline are unable to access education.

UNICEF Executive Director Catherine Russell said, "The continued shelling leaves little opportunity for Ukraine's children to recover from the distress and trauma associated with attacks."

She said education continues to be disrupted or out of reach for millions of Ukrainian children.