A Palestinian man mourns over the body of a child killed in an Israeli strike at the Nasser hospital in Khan Yunis on Thursday. AFP

The war has already killed over 20,000 Palestinians and driven around 85% of the population of 2.3 million from their homes. Much of northern Gaza has been levelled, and it has been largely depopulated and isolated from the rest of the territory for weeks. Many fear a similar fate awaits the south as Israel expands its offensive to most of the tiny enclave.

Israeli officials have brushed off international calls for a ceasefire — saying it would amount to a victory for Hamas.

The United States — while providing crucial support for the offensive — has urged Israel to take greater measures to spare civilians and allow in more aid. But humanitarian workers say the amount of food, fuel and medical supplies entering is still far below what is needed, and 1 in 4 Palestinians in Gaza are starving, according to UN officials.

An Israeli airstrike on a home in the northern town of Beit Lahiyeh — one of the first targets of the ground invasion that began in October — buried at least 21 people, including women and children, according to a family member.

Bassel Kheir Al Din, a journalist with a local TV station, said the strike flattened his family house and severely damaged three neighbouring homes. He said 12 members of his family — including three children aged 2, 7 and 8 — were buried and presumed dead, and that nine neighbors were missing.

In central Gaza, Israeli warplanes and artillery pounded the built-up Bureij and Nuseirat refugee camps, leveling buildings, residents said. Israel said this week it would expand its ground offensive into central Gaza, and typically launches waves of airstrikes and shelling before troops and tanks move in.

A hospital in the nearby town of Deir Al Balah received the bodies of 25 people killed overnight, including five children and seven women, hospital records showed on Thursday. Nonstop explosions could be heard throughout the night in the town - where hundreds of thousands of people have sought shelter, with many spending cold nights sleeping on sidewalks.

"It was another night of killing and massacres,” said Saeed Moustafa, a resident of the Nuseirat camp. He said people were still crying out from the rubble of a house hit by an airstrike on Wednesday.

"We are unable to get them out. We hear their screams but we don’t have equipment," he said.

Farther south, in Khan Younis, the Palestinian Red Crescent said a strike near its Al Amal Hospital killed at least 10 people and wounded another 12. Much of the city’s population has left, but many are sheltering near Al Amal and another hospital, hoping they will be spared from the bombardment.

Rami Abu Mosab, who lives in the Bureij refugee camp, said thousands of people have fled their homes in recent days because of the intense bombardment. He plans to remain there because he doesn't feel that anywhere in Gaza is safe.

"Here is death and there is death,” he said, "To die in your home is better.”

Bureij and Nuseirat are among several camps across the region that were built to house hundreds of thousands of Palestinian refugees from the 1948 war surrounding Israel's creation. They have since grown into crowded residential neighbourhoods.