More than 5,000 people have been evacuated from flood-damaged homes in northern Gaza and at least one person killed in what the United Nations called "a disaster area".
The flooding, caused by four days of torrential rain, was so severe that many homes could only be accessed by rowing boat with water two meters (more than six feet) deep in some places.
Severe weather in the form of heavy snowfall also paralyzed Palestinian cities such as Hebron in the occupied West Bank, as well as Jerusalem and parts of Israel's northern Galilee.
In Gaza, many people were trapped inside homes inundated by rising waters.
The Gaza health ministry said 100 people had been hurt as flood waters damaged poorly built homes in the coastal territory.
Chris Gunness, an UNRWA spokesman, said areas near a refugee camp in northern Gaza "have become a massive lake with two-meter-high waters engulfing homes and stranding thousands."
Thousands of agency workers were evacuating stranded Palestinians to U.N. shelters, Gunness said.
Gaza's Hamas government said 5,246 people in all had been evacuated to schools and other centers used as temporary shelters in the past four days.
Gaza's 1.8 million people have also endured daily blackouts of around 12 hours since the territory's lone power plant was switched off last month due to a fuel shortage.
One of the most densely populated tracts on earth, Gaza is home to mostly impoverished refugees and their descendants.
The territory lacks much basic civil infrastructure and lives under an Egyptian-Israeli blockade meant to cut off arms flows, but which also curbs imports of fuel, building supplies and basic goods.