An AFP correspondent reported one air strike east of Gaza City, and eyewitnesses reported a second in the centre of the city.
Witnesses also reported strikes in Nusseirat in central Gaza as well as in the Khan Yunis area in the south.
There were no immediate reports of deaths or injuries.
The raids came shortly after Israels army announced it was ending a ceasefire it had observed since 0600 GMT under the terms of an Egyptian truce proposal.
Hamas had effectively rejected the proposal, saying it was not consulted and would not halt fire without a broad deal that included concessions it has sought.
"Hamas has fired 47 rockets since we suspended our strikes in Gaza at 9:00 am. As a result, we have resumed our operation against Hamas," the army said on its official Twitter account.
"Following six hours of indiscriminate rocket fire at Israel, the IDF (army) has resumed operational activities against Hamas," military spokesman Lieutenant Peter Lerner said on his Twitter account.
Speaking on condition of anonymity, a senior Israeli official told AFP that the military had been ordered to "act forcefully".
"After Hamas and Islamic Jihad refused the Egyptian proposal for a ceasefire and fired dozens of rockets at Israel, the prime minister and defence minister have ordered the IDF to act forcefully against the terror targets in Gaza."
More than 192 people have been killed in Gaza over the past week as Israel has waged a relentless air campaign against Hamas militants.
In response, militants have fired more than a thousand rockets into Israel where no one has been killed in the current confrontation.(*)
Editor: Heru Purwanto
Copyright © ANTARA 2014
