Israeli warplanes launched a wave of air strikes on Hamas targets in the Gaza Strip, killing and injuring scores of Palestinians.
Medical officials say more than 227 Palestinians have been killed. Gaza officials and Hamas, the Islamic militant group that controls the Strip, say about 700 others were hurt in the attacks.
Missiles hit security compounds and militant bases across Gaza. Israel said the operation would go on "as long as necessary".
The wounded were ferried to hospital in cars and ambulances, while reports said the city's mortuaries were full.
Mosques in Gaza are calling on people to donate blood. Hamas sources said there was no room in the hospitals to treat victims.
A BBC producer in Gaza says people are desperately seeking refuge, but he says there are no safe places.
Israel said the strikes were in response to continued rocket fire by Palestinian militants against Israeli towns.
The strikes, the most intense Israeli attacks on Gaza in decades, come after the expiry of a truce with Hamas earlier this month.
Palestinian militants fired rockets in response to the air attacks on Saturday, killing one Israeli.
The air raids by Israel prompted protests in Gaza and beyond, including by Israeli Arabs in Nazareth.
Meanwhile, Israeli forces have been preparing equipment at bases near the Gaza border, reportedly for a possible ground attack.