Medics said most of the dead, including women and children, resulted from a barrage of Israeli air strikes on Wednesday that targeted several houses in the Jabalia area in northern Gaza.
The Israeli military had no immediate comment and said it was trying to verify the reports.
Israeli media reports on Wednesday cited security officials as saying they believed Hamas military leader Mohammad Sinwar and other senior officials had been killed in a strike on Tuesday.
The attack was on what the Israeli military described as a command-and-control bunker under the European Hospital in the southern city of Khan Younis.
There was no confirmation either from the Israeli military or Hamas.
On Wednesday, witnesses and medics said an Israeli air strike hit a bulldozer that approached the area of the strike at the European Hospital, wounding several people.
Late on Tuesday, Islamic Jihad, an Iranian-backed militant group in Gaza allied with Hamas, fired rockets towards Israel.
Shortly before the Israeli strikes began in response, the military issued evacuation orders to residents in the area of Jabalia and nearby Beit Lahiya.
The Israeli escalation came against Palestinian hopes the Trump visit might provide pressure for a de-escalation of violence.
Hamas on Monday released Edan Alexander, the last known living American hostage, before Trump's trip.
Speaking in Riyadh on Tuesday, Trump said more hostages would follow Alexander and added the people of Gaza deserved a better future.
Efforts to agree a ceasefire have faltered in recent weeks, with Hamas and Israel exchanging blame.
Hamas talked to the United States and Egyptian and Qatari mediators to arrange the release of Alexander, and Israel has sent a team to Doha to begin a new round of talks.
On Tuesday, Trump's special envoys Steve Witkoff and Adam Boehler met hostage families in Tel Aviv and said they could now see a better chance of an agreement for their release following the deal over Alexander.
The US has also presented a plan to reopen humanitarian aid deliveries in Gaza using private contractors.
Israel, which imposed a total blockade of supplies going into Gaza from March 2, has endorsed the plan.
But it has been rejected by the United Nations and international aid agencies and key details, including funding and donors, remain unclear.
Israel began its invasion of Gaza in retaliation for the Hamas-led attack on communities in southern Israel on October 7, 2023, that killed about 1200 people, according to Israeli tallies, and saw 251 taken as hostages into Gaza.
The Israeli campaign has killed more than 52,900 Palestinians, according to local health officials, and devastated the small coastal enclave.
Its population of about 2.3 million people is on the brink of famine, according to aid groups and international agencies.
