Israel has warned all residents of Gaza City to leave immediately in anticipation of a huge ground offensive.
The military's Arabic spokesman told as many as one million Palestinians living in Gaza's biggest urban centre to evacuate southwards. "Remaining in the area is extremely dangerous," he said.
On Monday, Israeli Prime Minister Benjamin Netanyahu said air strikes that had destroyed high-rise buildings in Gaza City in recent days were "only the beginning of the main, intensive operation" to capture what he has described as Hamas's last important stronghold.
Hamas said his remarks amounted to a "public demonstration of a fully-fledged crime of forced displacement".
Israel's plan to conquer Gaza City has also brought international criticism.
