Adnan Abu Hassna, the UN spokesman in Gaza told ITV News that the Israeli military attacked a school acting as a shelter at around half two this afternoon.
The Beit Hanoun elementary school had around 800 people, mostly women and children, inside when the attack took place.
Mr Hassna said the UN had provided the exact co-ordinates of the school to the Israeli military, so they are surprised by the attack.
The attack is thought to have come from a tank, or artillery. Local media are reporting 16 people have died and 10 have been injured.
ITV News, filming in the nearby Kamal Odwan hospital in Beit Hanoun, observed scores of injured children requiring treatment.