Around one million people have fled the Gazan city of Rafah in the past three weeks, the United Nations Palestinian refugee agency (UNRWA) said on Tuesday.
The small city on the southern edge of the Gaza Strip had been sheltering more than a million Palestinians who fled Israeli assaults on other parts of the enclave.
Since early May, Israel's military has been carrying out what it says is a limited operation in Rafah to kill fighters and dismantle infrastructure used by Hamas. It has told civilians to go to an "expanded humanitarian zone" some 20 kilometres away.
Many Palestinians have complained they are vulnerable to Israeli attacks wherever they go and have been moving up and down the Gaza Strip in the past few months.
UNRWA said the flight from Rafah "happened with nowhere safe to go and amidst bombardments, lack of food and water, piles of waste and unsuitable living conditions."
Providing assistance and protection is becoming nearly "impossible", the agency said.

Kenyan court charges 8 schoolgirls with fellow students' murder
At least 5 people killed in fire in Antwerp apartment block
Three people die in Mexico World Cup celebrations as fans crowd streets
US and Iran enter technical talks to secure peace deal, shipping restart
After Venezuela quakes, citizens lead rescues amid military theft accusations
Two dead after wildfire guts house in northern Greece
Afghanistan launches airstrikes on IS targets on border with Pakistan
Bangladesh warns of dengue surge as weather aids spread
