There was no immediate comment from the Israeli military, which has expanded its strikes on the enclave, killing hundreds of people since Thursday, in preparation for a new ground offensive to achieve "operational control" in parts of Gaza.
"We have at least 100 martyrs since overnight," Gaza health ministry spokesperson Khalil Al-Deqran told Reuters by phone on Sunday.
"Complete families were wiped off the civil registration record by Israeli bombardment."
Israel has blocked the entry of medical, food and fuel supplies into Gaza since the start of March to try to pressure Hamas into freeing Israeli hostages and has approved plans that could involve seizing the entire Gaza Strip and controlling aid.
Hamas says it will only free the hostages in return for an Israeli ceasefire.
Egypt and Qatar mediators, backed by the US, began a new round of indirect ceasefire talks between the two sides on Saturday but sources close to the negotiations told Reuters there had not been a breakthrough.
A Palestinian official close to the talks, which are taking place in the Qatari capital, Doha, said: "Hamas is flexible about the number of hostages it can free, but the problem has always been over Israel's commitment to end the war."
Britain's Sky News Arabica and the BBC both reported the Palestinian militant group had proposed releasing about half its Israeli hostages in exchange for a two-month ceasefire and the release of Palestinian prisoners held by Israel.
Contacted by Reuters, a Hamas official said: "Israel's position is unchanged, they want their prisoners released, without a commitment to end the war."
One of Israel's overnight strikes hit a tent encampment housing displaced families in Khan Younis in the southern Gaza Strip, killing women and children, wounding dozens and setting several tents ablaze.
Hamas described the strike as a "new brutal crime" and blamed the US administration for the escalation.
Among the dozens killed earlier on Sunday were three journalists and their families.
Medical officials said another family in northern Gaza lost at least 20 of its members.
Zakaria Al-Sinwar - the brother of former Hamas chief Yehya Al-Sinwar, who was killed by Israel in October - and three of his children were killed in an Israeli air strike on their tent in central Gaza Strip, medics said.
Sinwar was a history lecturer at a Gaza university.
The Gaza health care system is barely operational because of repeated Israeli bombardment and raids on hospitals.
The blockade on aid supplies has compounded their difficulties while adding to widespread hunger, for which Israel blames Hamas.
"Hospitals are overwhelmed with the growing number of casualties," Deqran said.
"Many are children, several cases of amputations, and the hospitals, which have been hit repeatedly by the occupation, are struggling with shortages of medical supplies."
The Israeli military said in a statement on Saturday it was conducting extensive strikes in areas of Gaza as part of its plan to reach its war objectives.
Israel's declared goal in Gaza is the elimination of the military and governmental capabilities of Hamas, which attacked Israeli communities on October 7, 2023, killing about 1200 people and seizing about 250 hostages.
The Israeli military campaign has devastated the enclave, pushing almost all residents from their homes and killing more than 53,000 people, according to Gaza health authorities.
