A woman who lost her son in an attack on a UN-run school in Gaza said there as "blood and screams" as shells hit the facility.

ITV News witnessed the aftermath of the attack at the Beit Hanoun elementary school, which was being used to shelter Palestinians from the heavy violence.

Laila Al-Shinbari said families had gathered to await evacuation when the shelling began.

"All of us sat in one place when suddenly four shells landed on our heads ... Bodies were on the ground, (there was) blood and screams. My son is dead and all my relatives are wounded including my other kids," she told Reuters.