In the evacuation order issued on Friday, the Israeli army instructed residents in the Bureij refugee camp and surrounding areas to "leave immediately for their own security" and head towards Deir al-Balah city further south.

"People in Gaza are people. They are not pieces on a checkerboard -- many have already been displaced several times," Thomas White, Gaza director for the UN's agency for Palestinian refugees, UNRWA, wrote on social media.

"The Israeli army just orders people to move into areas where there are ongoing air strikes. No place is safe, nowhere to go."

After the evacuation order, thousands of Palestinians fled the central Gaza Strip to the south on Friday.

UNRWA tweeted that the latest order would affect more than 150,000 people.

An estimated 1.9 million have been displaced by the war, according to the UN.

Fighting began on October 7 when Hamas gunmen broke through Gaza's militarised border and killed around 1,140 people in Israel, mostly civilians, according to an AFP tally based on Israeli figures.

Palestinian militants also abducted around 250 people during the attack, according to Israeli figures.

Vowing to destroy Hamas, Israel launched a relentless bombardment and ground invasion of Gaza, where 20,057 people have been killed, according to the latest toll from the territory's Hamas government.