The deadly exchange of fire between Palestinian militants in the Gaza Strip and the Israeli military has escalated significantly, with the UN fearing a “full-scale war”.
More than 1,000 rockets have now been fired by Palestinian militants over 38 hours, Israel said, most at Tel Aviv.
Israel has carried out hundreds of air strikes, destroying two tower blocks in Gaza on Tuesday and Wednesday.
At least 53 Palestinians and six Israelis have been killed since Monday.
That includes 14 Palestinian children caught up in the conflict.
UN Secretary-General António Guterres said he was “gravely concerned” by the ongoing violence.
An Israeli citizen was killed when an anti-tank guided missile, fired from the northern Gaza Strip, struck a jeep on the border. Three other people were injured.
The Israeli fatalities also reportedly include a 52-year-old father and his 16-year-old daughter who died in the city of Lod near Tel Aviv when a rocket hit their car.
In Gaza five members of one family were killed in an Israeli air strike. Streets are full of rubble where buildings have collapsed and cars have been left crushed or burned.
Israel says it has carried out operations to assassinate senior Hamas officials in Gaza.
Israeli Arabs have staged violent protests in a number of Israeli towns. Lod near Tel Aviv has been put under a state of emergency.
Prime Minister Benjamin Netanyahu said the government would use all its strength to protect Israel from enemies on the outside and rioters on the inside.
The fighting follows weeks of rising tension stoked by violent confrontations between Israeli police and Palestinian protesters culminating in clashes at a site in Jerusalem that is holy to both Muslims and Jews.
Israel’s military says the fighting is the most severe since the conflict in Gaza in 2014.
Of the 1,050 rockets and mortar shells that have now been fired from the Palestinian territory, 850 landed in Israel or were intercepted by its Iron Dome air defence system, and 200 failed to clear the border and landed back in Gaza, the Israeli army said.
Video footage from the city showed rockets streaking through the night sky, some exploding as they were hit by Israeli interceptor missiles.
Loud booms and air-raid sirens were heard across targeted cities, which included Tel Aviv, Ashkelon, Modiin and Beersheba, as Palestinian militants tried to overwhelm missile defences.
Anna Ahronheim, the defence and security correspondent of the Jerusalem Post, told the BBC: “To hear hundreds of interceptions and even to hear rockets fall near us was horrifying.”
The rocket fire escalated after the two residential tower blocks were brought down in Gaza. Israel said it was targeting rocket launch sites, high-rise buildings, homes and offices used by Hamas, the militant group that rules Gaza.
Hamas said it was incensed by “the enemy’s targeting of residential towers”.
Residents had been warned to evacuate the buildings before the fighter jets attacked, however health officials said there were still civilian deaths.
Fady Hanona, a journalist in Gaza City, tweeted a video he said showed explosion after explosion in Gaza on Wednesday morning.
“What is happening is unbelievable,” he said. “What we experienced this morning was more war than what we lived during the last three wars.”
The international community has urged both sides to end the escalation, amid concerns it could spiral out of control. The UN’s Middle East peace envoy, Tor Wennesland, said the sides were “escalating towards a full-scale war”.
Mr Guterres urged “a redoubling of efforts to restore calm”.
The chief prosecutor of the International Criminal Court (ICC), Fatou Bensouda, said she was watching the developments with “great concern” and that there might be crimes being committed under the ICC’s guidelines, which focus on crimes against humanity.