Palestinian officials in Gaza say Sunday was the deadliest day since the current fighting with Israel began.
More than 40 people were killed in the latest Israeli air strikes on Gaza, officials there say.
Israel’s army say Palestinian militants have fired more than 3,000 rockets at Israel over the past week.
United Nations Secretary-General António Guterres has warned that further fighting could plunge the region into an “uncontainable crisis”.
He pleaded for an immediate end to the “utterly appalling” violence.
Early on Monday, Israeli warplanes launched 80 air strikes on several areas of Gaza City, shortly after Hamas militants fired a barrage of rockets at southern Israel.
The UN has also warned of fuel shortages in Gaza which could lead to hospitals and other facilities losing power.
Lynn Hastings, UN deputy special co-ordinator for the Middle East Peace Process, told the BBC that she had appealed to Israeli authorities to allow the UN to bring in fuel and supplies but was told it was not safe.
Gaza officials said 42 people, including 16 women and 10 children, died in Sunday’s Israeli air strikes.
Ten people, including two children, have been killed in rocket attacks on Israel since the fighting began last Monday, Israel said.
The overall death toll in Gaza now stands at 188 people, including 55 children and 33 women, with 1,230 injured, according to the Hamas-controlled health ministry. Israel says dozens of militants are among the dead.
Israeli air strikes hit a busy street in Gaza just after midnight on Sunday, causing at least three buildings to collapse and dozens of deaths.
Hamas launched barrage of rockets towards southern Israel overnight and during the afternoon.
Millions of Israelis scrambled to safe rooms or shelters as sirens went off. Palestinians also tried to take precautions, but in the densely packed and poorly resourced Gaza Strip, many had nowhere to go.
Riyad Eshkuntana told Reuters news agency he put his daughters to sleep in a room of his house that he thought was the furthest from the explosions. Only one of his daughters, Suzy, six, survived the night. His wife and three other children died.
“I ran to check upon the girls,” said Mr Eshkuntana. “My wife jumped she hugged the girls to take them out from the room, then a second airstrike hit the room… The ceilings were destroyed and I was under the rubble.”
The Israeli military later said it had been conducted a strikes on a militant tunnel system in the area. The tunnels’ collapse caused the houses above to collapse as well, leading to unintended civilian casualties, it said.
Israel’s military says it has been targeting leaders and infrastructure linked to Hamas.
It said it had also struck the homes of Hamas leader Yahya Sinwar and his brother Muhammad Sinwar, whom it described as head of logistics and manpower for the movement.
It was unlikely they were at home at the time of the strikes, according to the Associated Press news agency.
Gazan rescue workers spent the day trying to rescue people from under the debris from the strikes.
The Palestinian health ministry said a doctor was among the dead: Dr Ayman Abu Al-Ouf, head of internal medicine at Shifa hospital and part of the coronavirus team. (Courtesy BBC)