Hospital officials in northern Gaza say many people have been killed in overnight Israeli air strikes.
Gazan rescue teams say search operations began early in the morning after Israel bombed at least five buildings in Beit Lahia and Gaza City.
Hamas-aligned media say dozens of people were killed and many are still buried in the rubble – including women and children.
There was no immediate comment from the Israeli military. It has recently intensified its offensive in northern Gaza, saying it is stopping Hamas from regrouping.
Parts of northern Gaza are under Israeli siege and virtually no humanitarian aid has been delivered in 40 days, the UN warned earlier.
Gazan medics say they are struggling to treat the injured, with aid agencies saying they cannot get essential supplies into the area.
Earlier this week, at least 34 people were killed in an Israeli air strike on a five-storey residential block in Beit Lahia, the local civil defence agency said.
The agency, quoted by AFP news agency, said many of the dead were women and children.
Israel’s ground offensive in northern Gaza has displaced up to 130,000 people over the past five weeks.
The UN says 75,000 people remain under siege with dwindling supplies of water and food in the towns of Beit Lahia, Jabalia and Beit Hanoun.
Last week’s report by Human Rights Watch said Israel had committed war crimes and crimes against humanity by deliberately causing the mass displacement of Palestinians in Gaza.
About 1.9 million people – 90% of Gaza’s population – have fled their homes over the past year, and 79% of the territory is under Israeli-issued evacuation orders, according to the UN.
Israel launched a campaign to destroy Hamas in response to the group’s unprecedented attack on southern Israel on 7 October 2023, in which about 1,200 people were killed and 251 others were taken hostage.
Nearly 44,000 people have been killed and more than 104,000 injured in Gaza since then, according to the territory’s Hamas-run health ministry.
On Wednesday, the US blocked a Gaza ceasefire draft resolution at the UN Security Council – the fourth time it has used its veto power during the conflict to shield its ally, Israel.
Fourteen of the 15 council members voted in favour of the draft, which demanded that the war in Gaza “must end immediately, unconditionally and permanently and all remaining hostages must be immediately and unconditionally released”.
Deputy US ambassador to the UN, Robert Wood, said the document “abandoned” the necessity for there to be “a linkage between a ceasefire and the release of hostages”.
Wood said the proposed resolution would have sent a “dangerous message” to Hamas.
In a separate development, US mediator Amos Hochstein has arrived in Israel from Beirut.
He has said that he sees a “real opportunity” to end the conflict in Lebanon after the Lebanese government and Hezbollah largely agreed to a US ceasefire proposal.
