Gaza’s Hamas-run health ministry says an Israeli air strike killed at least 70 people in the Al-Maghazi refugee camp in the centre of the strip.
A spokesman said the death toll was likely to rise given the large number of families living in the area.
The Israeli military told journalists it was looking into reports of the strike.
It comes as Israeli and Arab media say Egypt, which borders the Gaza Strip, has put forward a new proposal for a ceasefire between Israel and Hamas.
The Palestine Red Crescent Society says “intense” Israeli air strikes have led to the closure of main roads between Maghazi and two other refugee camps, Al-Bureij and Al-Nuseirat, “hindering the work of ambulances and rescue teams”.
In a statement, the Israeli military said it had received “reports of an incident in the Maghazi camp”.
It also said despite the challenges posed by Hamas terrorists operating within civilian areas in Gaza, the Israeli Defense Forces, IDF is committed to international law including taking feasible steps to minimize harm to civilians.
According to the health ministry, more than 20,000 people have been killed – mostly children and women – and 54,000 injured in Gaza since October 7, when Hamas and other Palestinian groups attacked Israel, killing 1,200 people and taking about 240 hostages.