Israeli forces bombarded Gaza City early on Monday and columns of tanks advanced into the heart of the city from different directions in what residents said was one of the heaviest attacks in the Palestinian territory since the start of the war.
The Gaza Civil Emergency Service said it believed dozens of people were killed but emergency teams were unable to reach them because of ongoing offensives in Daraj and Tuffah in the east and Tel Al-Hawa, Sabra and Rimal further west.
Residents said neighbourhoods in Gaza City, which lies in the north of the Gaza Strip, had been bombed throughout the night into the early morning hours. Several multi-floor buildings have been destroyed, they added.
One Israeli tank thrust pushed people towards the western road near the Mediterranean, residents said.
"The enemy is behind us, and the sea is in front of us, where we will we go?" said Abdel-Ghani, one Gaza City resident, who did not give his full name.
"Tank shells and missiles from the planes are falling on the roads and houses like hell from a volcano. People are running in all directions, and no one knows where to go," Abdel-Ghani told Reuters via a chat app.
The Israeli military said in a statement it was mounting an operation against Hamas infrastructure in the Gaza Strip.
The new Israeli offensive comes as Egypt, Qatar and the United States stepped up efforts to mediate a ceasefire agreement between Israel and Hamas as the Gaza war entered its tenth month.