Thousands of Palestinians have begun to flee their homes in the Gaza Strip after the Israeli military called for all civilians in the northern half of the besieged enclave to relocate south, as it amassed tanks for an expected ground assault.

The United Nations warned on Friday that the order demanding the relocation of 1.1 million people within 24 hours was “impossible” and could have devastating consequences.

The order, which comes on the seventh day of a war and “total blockade” declared by Israel following an unprecedented Hamas incursion and deadly attack, directs residents of Gaza City to flee deeper south into the Gaza Strip, a narrow coastal territory that is home to about 2.3 million people.

Palestinians in southern and central areas of the enclave, where people were expected to flee to, said air strikes had hit there overnight, with central parts also hit on Friday morning. “No place is safe in the entire Gaza Strip,” the Palestinian Red Crescent Society said.

According to Palestinian authorities, at least 1,799 people have been killed and more than 6,000 others wounded in Gaza since Israel launched a relentless bombardment of the territory on Saturday.

The UN humanitarian office (OCHA) said more than 400,000 people had already been made homeless in Gaza and 23 aid workers had been killed. “Mass displacement continues,” it said.