Israel has been shelling Gaza from the sea and air on the fifth day of its bombardment of the coastal territory.
One missile hit a media tower block in the centre of Gaza City, reportedly injuring six Palestinian journalists.
Israel says it still wants to hit hundreds of Gaza targets as it seeks to stop Hamas and other militant groups from firing rockets into Israel.
No Palestinian rockets or mortars had landed in Israel since midnight, the country's army said.
Militants on Saturday had 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.
Hospitals short on suppliesAt around 02:00 (00:00 GMT) on Sunday, the BBC's Jon Donnison in Gaza City reported hearing more than a dozen shells, 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.
At the scene
I live in a residential area close to lots of Hamas security buildings - the interior ministry is only 200m from my house - and we can hear bombings very close.
When Israel targets Hamas, civilians are always caught up in the cross-fire, and shelling from the sea is less accurate than aerial missile strikes.
People are exhausted after five days of bombing day and night.
Gaza has turned into a ghost city. Travelling during the night is very dangerous because Israeli drones are flying overhead.
Businesses, schools and universities are closed. The only people you find travelling around are ambulance drivers and journalists. People are only going out to buy food and fuel.
Our correspondent said a Hamas television station, al-Quds TV, was based in the media tower block, which had until last year housed the BBC's Gaza office. It was still being used by Sky News and ITN.
Israel said it had targeted "a communications antenna" in northern Gaza, as well as a Hamas training base, smuggling tunnels and underground rocket-launching sites.
Israel's leaders will need to decide what winning means and how far this operation will go, adds our correspondent.
Palestinian medical officials said one overnight strike had killed two infants from the same family.
The World Health Organisation says hospitals in Gaza are overwhelmed with casualties and short on supplies.
Egypt's president had said earlier there were "indications" a truce could be reached but that there were "no guarantees".
Mohammed Mursi was speaking in Cairo after meeting Turkish Prime Minister Recep Tayyip Erdogan. Hamas leader Khaled Meshaal is also in the Egyptian capital for the talks, aimed at de-escalating the conflict.
But Mr Mursi warned Israel against launching a ground offensive into Gaza.
Israel has put 75,000 reservists on stand-by, with one government minister being quoted as saying a ground offensive could be launched into Gaza on Sunday if the rocket fire does not stop.
Mr Mursi said: "If a ground invasion takes place... this will have serious repercussions for the region. We will never accept this and neither will the free world."
The Arab League has been holding an emergency meeting, also in Cairo, and announced it would send a delegation to Gaza in the next few days.
'Back to the Middle Ages'Israel's army says Operation Pillar of Defence has targeted more than 900 sites, while nearly 500 rockets fired from Gaza had hit Israel.
Another 257 missiles had been intercepted by its Iron Dome defence system, it added.
Sirens went off around Tel Aviv again on Saturday, with Israel's military saying Iron Dome had intercepted one missile fired from Gaza.
Interior Minister Eli Yishai was quoted by Israel's Haaretz newspaper as saying that the goal of the operation was "to send Gaza back to the Middle Ages. Only then will Israel be calm for 40 years".
Israeli military officials have said the bombardment of Gaza has inflicted heavy damage on Hamas, but suggested a ground invasion might be necessary to neutralise the group's military capability.
"Most of their weapons are stored in civilian's homes, they launch rockets from residential areas," said Maj Gen Tal Russo, Israel's southern commander.
"We do not want to hit civilians in Gaza but we do want to hit the hornets' nest of terror in Gaza."
Before the recent offensive, Israel had repeatedly carried out air strikes on Gaza as Palestinian militants fired rockets across the border.
But the aerial and naval bombardment is its most intense assault on the coastal territory since it launched a full-scale invasion four years ago.
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