A pregnant woman and her one-year-old daughter were among three people killed during Israeli air strikes along the Gaza Strip.
The Gaza Health Ministry said that a Hamas fighter and the two civilians were killed in separate incidents.
Their deaths come as violence continues to flare up between Israel and Gaza's rulers from the Islamic militant Hamas.
Since late on Wednesday, Gaza militants have fired dozens of rockets toward Israel, injuring several people.
An Israeli official said: "Hamas fired over 180 missiles into Israel overnight, injuring at least 23 people. Dozens of villages have been targeted, with thousands of families spending the night in bomb shelters."
Israel's military says it struck several Hamas targets in Gaza.
It was not clear if the escalation would derail Egyptian-brokered indirect negotiations between Israel and Hamas to reach a long-term ceasefire.
Gaza health officials identified those killed overnight as Hamas fighter Ali Ghandour, 23-year-old Enas Khamas and her daughter Bayan.