World leaders urged both sides to pull back from the edge and Joe Biden, facing his first major foreign policy test as US president, backed Israel and said he was hopeful the trading of airstrikes and rocket fire would end soon, following a phone call with Prime Minister Benjamin Netanyahu.
“My expectation and hope is this will be closing down sooner than later, but Israel has a right to defend itself,” Mr Biden told reporters after the call.
Events on the ground though could undermine any optimism about a swift end to the violence, the worst since 2014.
Earlier, Mr Netanyahu said his country would inflict blows on Hamas “that they couldn’t even dream of”. Benny Gantz, the Israeli defence minister, said his country was not preparing for a ceasefire and would stop military action only when it had achieved “complete quiet”.
Meanwhile, Hamas called for a full-scale intifada, or uprising.
Adding to the sense of a worsening situation getting further out of control, a state of emergency was ordered in the city of Lod, close to Tel Aviv, after protests by Israeli Arabs. Tensions on the streets were visible after shocking television footage on Wednesday night showed an Israeli Arab being dragged from his car and brutally attacked by a mob in the town of Bat Yam.
The death toll in the conflict reached 72, with 17 children among the lives lost.
All but two of the children were killed in Gaza, where 65 people have died during Israeli military action over the last three days. Palestinian health officials said another 365 have been wounded as a result of airstrikes.
Among the dead were a string of senior Hamas military figures, which Israel claims to have targeted and killed. The militant group confirmed the death of Bassem Issa, a Hamas commander, claiming they “took pride” in his “martyrdom”.
Israel’s military also suffered its first fatality on Wednesday, when 21-year-old Sergeant Omer Tabib “was killed as a result of anti-tank missile fire” from Hamas, officials said.
At least seven Israelis, including three women and two children, have been killed in fire from the blockaded strip. On Wednesday evening the municipality of Sderot announced that a five-year-old died of his wounds after being critically injured following an attack on the southern town.
The Israeli military said in total over 1,000 rockets had been fired by Hamas on Israel, including nearly a hundred which rained down on the Tel Aviv area on Tuesday night, over 70km away from Gaza, lighting up the sky.
The unprecedented barrage of rockets at times have been so intense it has overwhelmed Israel’s missile defences, causing air raid sirens to wail far further north of the country.
Israeli airstrikes have pounded areas of the Gaza Strip levelling two well-known apartment towers in the Gaza Strip.
The Israeli military said it sent warning shots and made calls to allow people to evacuate the buildings leading to no civilian casualties, but the material losses will be immense.
Israel faced heavy criticism over the tactic during the 2014 war,
Just after daybreak on Wednesday, Israel unleashed dozens of airstrikes in the course of a few minutes, targeting police and security installations, witnesses said.
The Hamas-run Interior Ministry said airstrikes destroyed the central police headquarters in Gaza City, a compound with several buildings. Lt Col Jonathan Conricus, a spokesperson for the Israeli military, said their strikes had targeted Hamas military intelligence and anti-tank commanders, as well as weapons stores and factories.
He said two infantry brigades were sent to the area, indicating preparations for a possible ground invasion.
Neither side showed signs of backing down: Hamas officials have linked the conflict to the status and situation in Jerusalem, a contested city that both sides claim as their capital.
Israeli military officials have spoken of an open-ended conflict. The Israeli cabinet is due to meet on Wednesday evening.
Boris Johnson joined multiple world leaders appealing for calm.
On Wednesday he urged both Israeli and Palestinian Leaders to “step back from the brink”, amid growing international fears that the conflict could escalate rapidly.
Calling for both sides to show restraint, he said “the UK is deeply concerned by the growing violence and civilian casualties and we want to see an urgent de-escalation of tensions”.
UN secretary-general Antonio Guterres said he was “gravely concerned” by the situation.
Tor Wennesland, the UN’s Middle East envoy, gave an even more ominous warning: “The cost of war in Gaza is devastating and is being paid by ordinary people. Stop the fire immediately. We’re escalating towards a full-scale war.”
Meanwhile, Turkey’s leader Recep Tayyip Erdogan called on the international community to give Israel a “strong and deterrent lesson” in a phone call with Russian leader Vladimir Putin.
The cross- border fighting is the dramatic crescendo to weeks of tensions that have simmered chiefly in the contested city of Jerusalem, that was captured by Israel in the 1967 Middle East war and effectively annexed later.
Violence between Palestinian protesters and Israeli security forces have centred around the Old City home to Temple Mount or Haram Ash-Sharif, the volcanic heart of the decades’ long conflict.
It reached breaking point after a controversial decision by Israel to evict four Palestinian families from the Sheikh Jarrah neighbourhood in occupied East Jerusalem in place of Israeli settlers.
The UN has said this order may amount to war crimes, and protests by Palestinians and Arab citizens of Israel rolled out across the country, East Jerusalem and the occupied West Bank.
But the cross border flare-up first erupted when on Monday, Hamas fired six long-range rockets towards Jerusalem, over 100km away, for the first time in seven years.
The group said it was in retaliation for Israeli forces storming al-Aqsa mosque, the third holiest site in Islam, multiple times with stun grenades and teargas.
The conflict edged towards a full-blown war when Hamas rained rockets down on Tel Aviv on Tuesday night in retaliation for an airstrike that levelled a prominent multi-storey bloc.
In Gaza, families described horrific scenes as airstrikes landed without warning in some areas.
“The children were playing around the home and their uncle was working near them, preparing the food for his animals. Suddenly the Israelis planes hit them, with no reason,” said Hag Hamza Almasri in the north of Gaza who lost several grandchildren in a strike.
“We are unarmed people. There were children. Why bomb us?” he asked.
In southern Israel, under an almost constant barrage of fire, panicked civilians repeatedly dashed for bomb shelters with some not able to make it in time.
“They can’t even direct their rockets, so they are firing at anywhere and everything, at civilians” said one man whose neighbour was killed in an airstrike in Ashkelon.
“The rockets have been non-stop.”