Five Gazans were killed in Israeli air strikes as militants fired around 250 rockets over the border, killing three Israelis, officials have said.
The latest violence raised to 13 the total number of Gazans killed in 20 hours of Israeli air strikes, which also left at least 120 people injured, medics said.
In the same period, Gaza rockets killed three Israelis and injured another five in a direct hit on a residential building in the southern town of Kiryat Malachi, police said.
Soon after dawn on Thursday, an Israeli air strike east of the southern Gaza Strip town of Khan Yunis killed three Palestinians, medical officials said.
The armed wing of Hamas, the Ezzedine al-Qassam Brigades, said that the three men were all members and were hit as they travelled in a motorcycle-taxi.
Later in the day an air strike hit northern Gaza, where two people were killed and another person was injured, medics said.
It was not immediately clear if they were civilians or militants.
Thursday's rocket strike in Kiryat Malachi "killed ... two males and a female in two apartments in a building which was hit," police spokesperson Micky Rosenfeld told AFP, saying another five people were injured, four lightly and one moderately.
'At least 195 rockets'
Since the violence erupted when Israel killed a top Hamas militant on Wednesday afternoon, the military has carried out "around 150 strikes" on Gaza, a spokesperson said.
In the same period, "at least 195 rockets" hit Israel while another 48 were intercepted by the Iron Dome anti-missile system.
The bloodshed began at around 14:00 GMT on Wednesday when Israel killed Hamas military chief Ahmed Jaabari and his bodyguard, sparking a fierce bout of cross border fighting which continued into the night.
Six more people died during various strikes later on Wednesday, including two children, officials from the Hamas-run health ministry said as Gaza hospitals went on high alert.
Meanwhile, British Foreign Secretary William Hague has said that Hamas "bears principal responsibility" for the current crisis in Gaza, and that it should cease attacks against Israel immediately.
He also strongly urged Israel to do its "utmost" to reduce tensions, avoid civilian casualties and help create the conditions for peace, warning: "It is imperative to avoid the risk of a spiral of violence."— Sapa-AFP.