Three people were killed in an Israeli air strike on a house in the Sabra suburb in Gaza City, while another air strike left two men dead and wounded six others in Beit Hanoun town in the north, the Gaza health officials said.
The Israeli military said it struck a Hamas site in northern Gaza, where they detected preparations for firing into Israeli territory.
Israel resumed air strikes a day earlier as both sides traded blame over breaking a ceasefire and shattering nearly two months of relative calm.
Israeli naval vessels attacked several boats it said were intended to carry out "terrorist" acts by Hamas and Islamic Jihad militant groups.
Palestinians said an Israeli drone fired at several fishing boats onshore of Gaza City, setting several of them ablaze.
On Wednesday, the Israeli army dropped leaflets on areas in Beit Hanoun and Khan Younis in the northern and southern Gaza Strip, ordering residents to evacuate their homes warning them they were in "dangerous combat zones".
"Staying in the shelters or the current tent put your lives and that of your family members in danger, evacuate immediately," a leaflet dropped on Beit Hanoun said.
Israeli air strikes on Tuesday left more than 400 people dead, according to Palestinian health authorities, and Israel warned the onslaught was "just the beginning".
Israel and Hamas accuse each other of breaching the truce, which had broadly held since January and offered respite for the 2.3 million inhabitants of Gaza, which has been reduced to rubble.
Israeli Prime Minister Benjamin Netanyahu said he ordered strikes because Hamas had rejected proposals to secure a ceasefire extension.
Hamas, which still holds 59 of about 250 hostages Israel says the group seized in its October 7, 2023, cross-border attack, accused Israel of jeopardising efforts by mediators to negotiate a permanent deal to end the fighting.
Hamas officials said they remained keen on concluding the three-phase ceasefire deal as signed.
Hamas-led gunmen attacked Israel that day, killing about 1200 people and taking the hostages, according to Israeli tallies.
The Israeli campaign in Gaza has killed more than 48,000 people, say Palestinian health authorities.
