Gaza's civil defence agency said on Tuesday that an overnight Israeli air strike killed more than 55 people in a residential building in the northern district of Beit Lahia.
"More than 55 people have been martyred and dozens more wounded are under the rubble of a five-storey residential building belonging to the Abu Nasr family that was hit by the Israeli occupation last night in Beit Lahia," agency spokesman Mahmud Bassal told AFP.
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.
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 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.
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 members 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 fighters.
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.
