Palestinians are streaming out of eastern Khan Younis, the second-largest city in Gaza, as an Israeli evacuation order affects roughly 250,000 people, the United Nations said Tuesday.

Although the exact number of people fleeing was not immediately known, Sigrid Kaag, the top U.N. humanitarian official for Gaza, said more than 1.9 million people are displaced inside the war-torn enclave. Israel’s military estimated that about the same number of people — around 80% of all Palestinians in the Gaza Strip — are now clustered into the territory’s central region.

Israel's military on Monday instructed Palestinians to evacuate a wide swath of Khan Younis and nearby areas, ordering them to head to an Israeli-declared safe zone. That suggests Israel will launch a new ground assault into the city.

However, an Israeli strike on a house inside the safe zone Tuesday killed at least 12 people, including nine members of the same family. Some of the dead had just fled Khan Younis hours earlier, said Asmaa Salim, a relative who lived in the targeted building in Deir al-Balah. The Israeli military did not immediately comment on the strike.

Evacuees have been told to seek refuge in sprawling tent camps in a coastal area that's already overcrowded and has few basic services. The war has largely cut off the flow of food, medicine and goods to Gaza, and people there are now totally dependent on aid.

Israel launched the war in Gaza after Hamas’ Oct. 7 attack, in which militants stormed into southern Israel, killed some 1,200 people — mostly civilians — and abducted about 250.

Since then, Israeli ground offensives and bombardments have killed more than 37,900 people in Gaza, according to the territory's Health Ministry, which does not distinguish between combatants and civilians in its count. The top U.N. court has concluded there is a “plausible risk of genocide” in Gaza — a charge Israel strongly denies.