An Israeli airstrike killed at least five Palestinians in an apartment building in Gaza City early on Saturday, health and civil defence service officials said.
The strike destroyed the apartment building and started a fire.
There was no immediate comment from the Israeli military.
"We were asleep and suddenly heard continuous strikes, and heavy explosions, the children woke up startled and started running and screaming," said eyewitness Ahmed Al-Dahdouh.
"We ran out and found that our neighbour's house was struck," he told Reuters.
Last year's US-brokered Gaza ceasefire calls for eventual reconstruction of the territory. But little progress has been made towards implementing a deal to end the conflict that includes terms for Hamas to disarm and Israel to withdraw its troops.
Israel, which says Hamas has been rearming and launching attacks in violation of the ceasefire, has stepped up strikes on the group in recent weeks.
Hamas has denied trying to carry out attacks or rebuild its arsenal and accuses Israel of undermining the Gaza peace deal.
Gaza health officials have said at least 1,400 Palestinians have been killed by Israeli fire since last October's ceasefire. Israel says four of its soldiers have been killed by fighters in Gaza over the same period.
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