The UN Relief and Works Agency, or UNRWA, which serves over one million Palestinians in Gaza, has directed the displaced to one of its schools for "protected shelter", offering them mattresses, blankets and some kitchen tools.
There has been no massive displacement so far, Filippo Grandi, UNRWA's Commissioner General, told Reuters during a visit to a distribution centre in the Gaza Strip.
"What usually triggers displacement is a ground operation, a ground offensive. That's why we really hope that a ground offensive will not happen because among many other things it will also cause a lot of humanitarian problems," Grandi said.
Egypt is trying to mediate a ceasefire between Israel and the Islamist Hamas movement, which controls Gaza. The Israelis say they would prefer a negotiated truce but are prepared for wider military action if there is no acceptable agreement.
Israeli forces are formally instructed to avoid civilian targets. But more than a half of the 115 Palestinians killed so far were civilians, including 27 children. Street-to-street urban fighting could raise the toll significantly.
Three Israeli civilians have so far been killed in one rocket attack in an Israeli city north of Gaza and more than 60 people have suffered injuries.
Human rights groups said Israeli air strikes on inhabited houses in Gaza have increased in the past two days. The deadliest killed nine members of one family on Sunday.
Many Gazans believe Israel is deliberately targeting houses to mount pressure on Hamas to cease fire.
Israel says it takes great care to avoid civilian casualties and accuses Hamas and other militant groups of deliberately placing Gaza's 1.7 million people in harm's way by placing rocket launchers among them.
Nael al-Attar, 28, said he had fled his house with his wife and two children "under fire from the Israeli army."
"The Jews killed children, the elderly and women. We hope this does not last long and we urge all countries to intervene and resolve the conflict," Attar said.
But he added: "We thank Hamas and all other organizations for their resistance. Do all you can to terrorise the occupier."
Israel withdrew settlers and armed forces from Gaza in 2005 but has maintained a blockade of the tiny, overcrowded enclave.
GAZA CITY (Reuters) -- At least 50 Gaza families living next to the front line with Israel had fled their homes by the seventh day of Israel's air war but far more people will be uprooted if there is any ground invasion, the UN relief agency in the enclave said on Tuesday.