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 U.N. aid agency said on Tuesday.

About 47,000 of the displaced people have sought shelter in 58 U.N.-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.

The U.N. 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