Gaza's civil defence agency said Tuesday that an overnight Israeli air strike killed 93 people in a residential building in the northern district of Beit Lahia.
"The number of martyrs in the massacre of the Abu Nasr family home in Beit Lahia has risen to 93 martyrs, and about 40 are still missing under the rubble," agency spokesman Mahmud Bassal told AFP in an updated toll.
The Israeli military said it was "looking into the reports".
"The explosion happened at night and I first thought it was shelling, but when I went out after sunrise I saw people pulling bodies, limbs and the wounded from under the rubble," said Rabie al-Shandagly, 30, who had taken refuge in a nearby school in Beit Lahia.
"Most of the victims are women and children, and people are trying to save the injured, but there are no hospitals or proper medical care," he told AFP.
On Tuesday, Palestinians searched through the rubble of the building and removed the dead, while others mourned over the bodies of relatives.
In one AFP image, a charred body with long hair hung out of a window of the building in Beit Lahia.
An AFP journalist saw several bodies wrapped in white shrouds, blankets and sheets as rescuers and relatives pulled them from the rubble of the building.
Relatives were also seen burying bodies, while rescuers continued to search the rubble for survivors.
"The enemy has committed another horrific massacre against our people, and northern Gaza is being subjected to a campaign of ethnic cleansing and systematic displacement," Hamas said in a statement condemning the Beit Lahia attack.
The bodies of 15 people killed in the strike were brought to Kamal Adwan Hospital, its director Hussam Abu Safia told AFP.
He said 35 wounded people, most of them children, were being treated at the hospital.
"We are still receiving a number of martyrs and wounded," Safia said, adding that the hospital was struggling to treat patients due to a lack of staff and medicines.
"There is nothing left in the Kamal Adwan Hospital except first aid materials after the army arrested our medical team and workers when they invaded the hospital during the military operation in Jabalia," Safia said.
Last week, the Gaza health ministry said Israeli troops had stormed the hospital, while the Israeli military said it was operating around it.
The World Health Organization said its teams managed to return to Kamal Adwan hospital on Monday and provided information about the situation there.
"They have found one orthopaedic surgeon, one paediatrician, a chief nurse and a handful of young doctors, and junior doctors and nurses try to attend to some 100-150 patients," WHO spokesman Tarik Jasarevic told reporters in Geneva on Tuesday.
"This shows how difficult it is to provide any sort of aid in north Gaza."
Since October 6, the military has conducted a sweeping air and ground assault in northern Gaza, particularly in the areas of Jabalia, Beit Lahia and Beit Hanoun, in what it describes as an operation to prevent Hamas militants from regrouping.
In a statement issued on Tuesday morning, the military said it had carried out several ground and air strikes in Jabalia over the past day, killing around 40 militants.
Tens of thousands of Palestinians have been forced to flee northern Gaza since the onslaught began, while the civil defence agency has reported hundreds of deaths.
