Renewed fighting in Gaza stretched into a second day on Saturday after talks to extend a week-old truce with Hamas collapsed and mediators said.
Israeli bombardments were complicating attempts to again pause hostilities.
Eastern areas of Khan Younis in southern Gaza came under intense bombardment as the truce deadline lapsed shortly after dawn on Friday, with columns of smoke rising into the sky, Reuters journalists in the city said.
Residents took to the road with belongings heaped up in carts, searching for shelter further west. Israel said its ground, air and naval forces struck more than 200 "terror targets" in Gaza.
By Friday evening, health officials in the coastal strip said Israeli strikes had killed 184 people, wounded at least 589 others and hit more than 20 houses.
The warring sides blamed the other for the truce collapse by rejecting terms to extend the daily release of hostages militants in exchange for Palestinians held in Israeli jails.
The United Nations said the fighting would worsen an extreme humanitarian emergency. "Hell on Earth has returned to Gaza," said Jens Laerke, spokesperson for the U.N. humanitarian office in Geneva.
"Today, in a matter of hours, scores were reportedly killed and injured. Families were told to evacuate, again. Hopes were dashed," said U.N. aid chief Martin Griffiths, adding that children, women and men of Gaza had "nowhere safe to go and very little to survive on."
A pause that started on Nov. 24 had been extended twice and Israel had said it could continue as long as Hamas released 10 hostages each day.
But after seven days during which women, children and foreign hostages were freed, mediators failed to find a formula to release more.
Israel accused Hamas of refusing to release all the women it held.
Qatar, which has played a central mediating role, said negotiations were still going on with Israelis and Palestinians to restore the truce, but Israel's renewed bombardment of Gaza had complicated matters.
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