More than 123,000 people have been displaced in the Gaza Strip since the outbreak of the conflict between Palestinian militants and Israel, the United Nations said on Monday.

"Over 123,538 people, have been internally displaced in Gaza, mostly due to fear, protection concerns and the destruction of their homes," said the UN's humanitarian agency, OCHA.

More than 73,000 are sheltering in schools, OCHA said, some of which have been designated emergency shelters.

Israel has launched hundreds of strikes on Gaza since Saturday, when Hamas militants launched deadly attacks in Israel and fired thousands of rockets at the country.

Adnan Abu Hasna, a spokesman for the UN agency for Palestinian refugees, said he expected the numbers to rise further.

"There's electricity in these schools, we provide them with a meal, clean water, psychological support and medical treatment," he told AFP.

Gaza is home to 2.3 million Palestinians, who have lived under a crippling Israeli blockade imposed after Hamas took power in 2007.