Fighting has resumed in Gaza after the seven-day temporary ceasefire between Israel and Hamas expired.
The Israeli military has dropped leaflets warning residents in parts of southern Gaza to flee for their safety as bombing resumes.
Both sides have blamed each other for the violence restarting after a week in which more than 100 hostages were released by Hamas in exchange for 240 Palestinian prisoners in Israeli jails.
The Hamas-run health ministry in Gaza says dozens of people were killed on Friday morning.
Rockets have also been fired into southern Israel from Gaza.
Earlier, the US warned Israel that the "massive loss of civilian life" seen in northern Gaza should not be repeated in the south.
Hamas attacks on Israel on 7 October killed 1,200 people with around 240 others taken hostage.
Since then, Gaza's Hamas-run health ministry says more than 14,800 people have been killed in Israel's retaliatory campaign, including about 6,000 children.
