Israeli strikes killed 42 Palestinians in the Gaza Strip on Sunday, the worst daily toll in almost a week of deadly clashes, as UN Security Council talks fizzled despite global alarm at the escalating conflict.

Israeli warplanes continued to pummel the Palestinian enclave overnight Sunday to Monday, carrying out dozens of air strikes across the densely populated territory in just a few minutes and causing power cuts, AFP journalists said.

The Israeli army said in the first hours of Monday its fighter jets were "striking terror targets in the Gaza Strip". 

UN Secretary-General Antonio Guterres pleaded for an immediate end to the "utterly appalling" violence and warned of an "uncontainable security and humanitarian crisis".

But the council meeting, already delayed by Israel's ally the United States, resulted in little action.

The heaviest exchange of fire in years -- sparked by unrest in Jerusalem -- has killed 197 in Gaza and 10 in Israel since Monday, according to authorities on either side. 

This picture taken from the southern Israeli city of Sderot shows rockets fired from the Gaza Strip being intercepted by the Israeli Iron Dome missile defence system.

Israel said Sunday morning its "continuing wave of strikes" had in the past 24 hours struck over 90 targets across the coastal enclave, where an Israeli strike that destroyed a building housing journalists' offices sparked international outrage.

The death toll kept rising in Gaza as rescuers extracted bodies from vast piles of smoking rubble and the bereaved wailed in grief.

"We were sleeping and then all of a sudden there were rockets raining down on us," said Lamia al-Koulak, 43, who lost relatives in a dawn bombardment.

"The children were screaming. For half an hour we were bombarded without prior warning. We came out to find the building next door flattened."

Israeli Prime Minister Netanyahu said the campaign would "take time" to finish.

"Our campaign against the terrorist organisations is continuing with full force," he said in a televised address. "We are acting now, for as long as necessary, to restore calm and quiet to you, Israel's citizens."

'Hatred and revenge' 

Israel's army said about 3,000 rockets had been fired since last Monday from Gaza towards Israel -- the highest rate ever recorded. 

Around 450 fell within the coastal strip, while the Iron Dome anti-missile system intercepted over 1,000, according to the army.

Rockets have wounded over 280 people, hitting districts previously well beyond the range of Hamas' rockets.

Army chief Aviv Kochavi said Israel had reacted with unprecedented force.

"Hamas misjudged the strength of our response," he said.

Two doctors and at least 58 children have died in Gaza, local health authorities said. More than 1,200 people have been wounded and entire city blocks smashed to rubble.

Gaza health authorities said 40,000 people had been displaced from their homes, and the head of the UN agency for Palestinian refugees, Philippe Lazzarini, announced over 40 of UNRWA's schools had been converted into shelters.  

Save the Children warned that life-saving services were "at breaking point" after Israeli strikes damaged power lines.

The Israeli army says it takes all possible precautions to avoid harming civilians, and blames Hamas for deliberately placing military targets in densely populated areas.

Palestinian foreign minister Riyad al-Maliki urged the Security Council to act, accusing Israel of "war crimes and crimes against humanity".

But Israel's UN ambassador blamed Gaza militants for the bloodshed.

"It was completely premeditated by Hamas in order to gain political power," Gilad Erdan said.

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This is not a sunrise. But another bomb dropped on Gaza. pic.twitter.com/7TvZ5WGVeK

— Khaled Beydoun (@KhaledBeydoun) May 17, 2021

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Media offices destroyed 

The Israeli army said it had targeted the infrastructure of Hamas and Islamic Jihad, including a vast tunnel system, weapons factories and storage sites.

Israeli air strikes also hit the home of Yahya Sinwar, head of Hamas's political wing in Gaza, the army said, releasing footage of plumes of smoke and intense damage, but without saying if he was killed.

Balls of flame and a cloud of debris shot into the sky Saturday afternoon as Israel's air force flattened a building housing Al Jazeera and AP news agency, after giving journalists an hour to evacuate. 

Netanyahu on Sunday defended the strike, alleging the building also hosted a Palestinian "terrorist" intelligence office.

AP called for an independent investigation. Al Jazeera's Jerusalem bureau chief, Walid al-Omari, accused Israel of trying "to silence media that are witnessing, documenting and reporting the truth". 

Media watchdog Reporters Without Borders called on the International Criminal Court to determine whether the strike on a building housing media outlets constitutes war crimes.

'It was hell' 

The cross-border fire has sparked inter-communal violence between Jews and Arab-Israelis, as well as deadly clashes in the occupied West Bank, where 19 Palestinians have been killed since Monday.

A rocket on Sunday damaged a synagogue in the southern Israeli city of Ashkelon, shortly before prayers for the Shavuot Jewish holiday.

And a car-ramming attack wounded seven police officers in the flashpoint Sheikh Jarrah neighbourhood of Israeli-annexed east Jerusalem, police said, adding that the attacker had been "neutralised".

Sheikh Jarrah has been at the heart of the flare-up, seeing weeks of clashes between Palestinians and Israeli security forces who have cracked down on protests against the planned expulsion of several Palestinian families from their homes there.

Palestinians have also been outraged by police actions against worshippers protesting at Jerusalem's Al-Aqsa mosque compound.

China on Sunday accused the US of blocking a Security Council statement on the violence.

"Simply because of the obstruction of one country, the Security Council hasn't been able to speak with one voice," said Foreign Minister Wang Yi.

The United States, Israel's main ally, had already delayed the Council session and shown little enthusiasm for a resolution.

President Joe Biden's administration says it is working behind the scenes and that a Security Council statement could backfire.

US Secretary of State Antony Blinken on Sunday spoke to officials in Qatar, Saudi Arabia, Egypt and France, according to the State Department, reiterating calls to end the violence.

The Biden administration has publicly backed Israel's right to self-defence, while urging de-escalation.