Israel has been shelling Gaza from the sea and air on the fifth day of its bombardment of the coastal territory.
The Israeli military says there was a lull in Palestinian rocket and mortar fire overnight but the attacks on Israel have resumed.
It says that in the last four days, nearly 500 rockets fired from Gaza had hit Israeli territory.
Another 257 had been intercepted by its Iron Dome defence system.
Missiles hit two media buildings in the centre of Gaza City, injuring several Palestinian journalists.
Palestinian medical officials said one strike killed two infants from the same family.
The Middle East Foreign Press Association has asked the Israeli military why two buildings housing journalists were hit.
On Saturday, militants in Gaza fired dozens of rockets into Israel, including one at Tel Aviv that was intercepted.
Health officials in Gaza say 48 Palestinians have been killed since Israel launched Operation Pillar of Defence on Wednesday with an air strike that killed Hamas military chief Ahmed Jabari.
Three Israelis were killed on Thursday.
A BBC correspondent in Gaza City reported hearing more than a dozen shells at about 2am on Sunday, apparently fired from Israeli war ships - a new development in the five day bombardment.
Artillery fire is less generally accurate than air strikes, which were also heard across Gaza City throughout the night.
The World Health Organisation says hospitals in Gaza are overwhelmed with casualties and short on supplies.