Emergency services spokesman Ashraf al-Qudra said the 70 injured included at least 20 hospital staff, among them doctors.
He said the third floor of the Al-Aqsa Martyrs hospital in Deir al-Balah had been hit, with an interior ministry official saying it was hit by Israeli tank fire.
Palestinian television showed footage of wounded people, including medical staff, being treated after the bombing.
In other event, an Israeli air strike Monday on a home in the center of Gaza City killed eight people, including four children, Palestinian medics said.
The new strike came shortly after Israeli shelling of a central Gaza hospital, emergency services spokesman Ashraf al-Qudra told AFP.
NJF/NJF