A woman reacts while standing near the rubble of a building that was destroyed by an Israeli airstrike in Gaza City. AP

More than 52,000 Palestinians have been displaced by Israeli air strikes that have destroyed or badly damaged nearly 450 buildings in the Gaza Strip, the UN aid agency said on Tuesday.

Palestinians across Israel and the occupied territories went on strike in a rare collective action against Israel's policies on Tuesday as Israeli strikes rained down on Gaza and Hamas group fired dozens of rockets from the Hamas-ruled territory.

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At least 213 Palestinians have been killed in heavy airstrikes since, including 61 children and 36 women, with more than 1,440 people wounded, according to the Gaza Health Ministry, which does not break the numbers down into fighters and civilians.

A man carries a dead child taken out of the rubble of a destroyed residential building in Gaza. AP

As the fighting drags on, medical supplies, fuel and water are running low in Gaza. Ten people in Israel, including a 5-year-old boy and a soldier, have been killed in the ongoing rocket attacks launched from civilian areas in Gaza toward civilian areas in Israel.

About 47,000 of the displaced people have sought shelter in 58 UN-run schools in Gaza, Jens Laerke, spokesman of the United Nations Office for the Coordination of Humanitarian Affairs (OCHA), told reporters.

Laerke said 132 buildings had been destroyed and 316 had been severely damaged, including six hospitals and nine primary healthcare centres, according to Reuters.

The UN agency said it welcomed the fact that Israel had opened one border crossing for humanitarian supplies but called for another crossing to also be opened.

Palestinians inspect their house, after it was destroyed by an Israeli airstrike. AFP

With the war in Gaza showing no sign of abating and truce efforts apparently stalled, the general strike and expected protests could again widen the conflict after a spasm of communal violence in Israel and protests across the occupied West Bank last week.

Tuesday's airstrikes toppled a six-story building that housed libraries and educational centers belonging to the Islamic University, leaving behind a massive mound of rebar and concrete slabs. Desks, office chairs, books and computer wires could be seen in the debris. Residents sifted through the rubble, searching for their belongings.