Israeli tanks battled their way to the centre of Khan Younis on Sunday in a major new push into the heart of the main city in the southern Gaza Strip.

Residents said tanks had reached the main north-south road through the middle of Khan Younis after intense combat through the night that had slowed the Israeli advance from the east. Warplanes were pounding the area west of the assault.

The air rumbled with the constant thud of explosions and thick columns of white smoke rose over the city, which is sheltering hundreds of thousands of civilians who fled other parts of the enclave. As morning broke near a city-centre police station, the constant rattle of machinegun fire could be heard. Streets there were deserted apart from an old woman and a girl riding on a donkey cart.

“It was one of the most dreadful nights, the resistance was very strong, we could hear gunshots and explosions that didn’t stop for hours,” a father of four displaced from Gaza City and sheltering in Khan Younis told Reuters.

“In Khan Younis tanks reached Jamal Abdel-Nasser Street, which is at the centre of the city. Snipers took positions on buildings in the area,” he said.

Israel launched the storm of Khan Younis this week after a truce collapsed, extending its ground war to Gaza’s southern half in a new, expanded phase of its two-month-old campaign to wipe out Hamas militants. International aid organisations say this has left the enclave’s 2.3 million people with nowhere to hide.

At the site of one Khan Younis home that had been destroyed by bombing overnight, relatives of the dead were combing the rubble in a daze. They dragged the body of a middle-aged man in a yellow T-shirt from under the masonry.

“We prayed the nighttime prayer and went to sleep, then woke up to find the house on top of us. ‘Who’s alive?!’” said Ahmed Abdel Wahab.

“The civil defence forces came and rescued who they could, and this is what’s left. Three floors above collapsed and the people are under it. God is our saviour and the disposer of our affairs. My mother and father, my sister and brother, all of my cousins.”

Militant group Islamic Jihad, allied to Gaza’s Hamas rulers, said its fighters were battling Israeli forces in the area. The Israeli military said it bombed underground tunnel shafts in Khan Younis and attacked a squad of Palestinian gunmen preparing an ambush, but said nothing about any tank advance there.

Both sides also reported heavy fighting in the north of the Gaza Strip, where Israel had previously said its troops had mainly succeeded in their mission last month. Explosions rang out at dawn there and columns of smoke could be seen from across the fence in Israel.