Gaza rescue teams and medics said Israeli air strikes killed at least 55 people on Thursday, as the military threatened an even larger offensive if hostages were not freed soon.

Israel resumed its military assault in the Gaza Strip on March 18, after the collapse of a two-month ceasefire that had brought a temporary halt to fighting in the blockaded Palestinian territory.

Israel's army chief, visiting troops in Gaza on Thursday, threatened to expand the offensive in Gaza if hostages seized during Hamas's October 7, 2023 attack on Israel were not released.

"If we do not see progress in the return of the hostages in the near future, we will expand our activities to a larger and more significant operation," Lieutenant General Eyal Zamir said.

The warning came as the army issued fresh evacuation orders for northern areas of Gaza ahead of a planned attack.

Earlier in the day, six members of one family – a couple and their four children – were killed when an air strike levelled their home in northern Gaza City, the civil defence agency said in a statement.

Nine people were killed and several wounded in another strike on a former police station in the Jabalia area of northern Gaza, according to a statement from the Indonesian Hospital, where the casualties were taken.

"Everyone started running and screaming, not knowing what to do from the horror and severity of the bombing," said Abdel Qader Sabah, 23, from Jabalia.

Israel's military said it struck a Hamas "command and control centre" in the area but did not say whether it was the police station.

In another deadly attack, the bodies of 12 people were recovered after the Hajj Ali family home, also in Jabalia, was struck, the civil defence said.

Another 28 people were killed in strikes across the territory, medics and the civil defence agency reported.

They came as the Israeli military ordered Palestinians living in the northern areas of Beit Hanoun and Sheikh Zayed to evacuate ahead of an attack.

The United Nations has warned that Israel's expanding evacuation orders across Gaza are resulting in the "forcible transfer" of people into ever-shrinking areas.

Aid agencies estimate that the vast majority of Gaza's 2.4 million residents have been displaced at least once since the war began. (AFP)