Israeli warplanes pounded Gaza Wednesday, killing at least 30 people in a major new confrontation with Palestinians, as Hamas flexed its firepower and sent thousands running for shelters across the country.

As the death toll from Israel's two-day Operation Protective Edge reached 57, Palestinian president Mahmoud Abbas accused Israel of committing "genocide" in Gaza.

But Israeli Prime Minister Benjamin Netanyahu appeared bent on ploughing ahead, warning of even tougher action against Hamas.

There have been no Israeli deaths so far, but Hamas began flaunting its firepower overnight. It launched waves of long-range rockets across central Israel that triggered sirens in cities as far away as Tel Aviv and Jerusalem.

The alarms even sounded in the northern port city of Haifa, as unconfirmed reports spoke of a rocket hitting near Caesarea and another even further north.

Tanks massed on the Gaza border, AFP correspondents reported, as Netanyahu came under mounting pressure from hardliners within his governing coalition to send ground forces into the territory from which it pulled all troops and settlers in 2005.

"We have decided to further intensify the attacks on Hamas and the terror organisations in Gaza," his office quoted him as saying.

President Shimon Peres warned that, "if the fire continues we do not rule out a ground incursion," his office quoted hims as saying in an interview with CNN.

This "may happen quite soon," said Peres, who retires later this month.

The escalation comes with Arab riots inside Israel over the burning to death of a Palestinian teenager by Jewish extremists and the region in flames, with civil war raging in neighbouring Syria and conflict intensifying in Iraq.

The European Union and the United States both called for restraint in the confrontation.

It came as the Palestinians moved towards greater unity following a reconciliation agreement between Hamas and Abbas that ended seven years of rival administrations.

That deal came after nearly a year of US-brokered peace negotiations between Israel and the Palestinians collapsed, to the satisfaction of Netanyahu's hardline coalition partners.

The Palestinian teenager was murdered in apparent revenge for the kidnap on June 12 of three Israeli youths in the occupied West Bank, who were subsequently killed.

Their abductions sparked a huge Israeli assault on Hamas's infrastructure in the territory and retaliatory rocket fire from the Islamists' Gaza power base.

Six women and nine children were among at least 30 Palestinians killed in Israeli strikes on Gaza on Wednesday, medics said.

The deadliest single strike took place shortly after midnight when a missile slammed into a house in northern Gaza, killing an Islamic Jihad member and five of his family members.

Raids to the north and east of Gaza City killed two women and four children, while a strike on Maghazi refugee camp in central Gaza killed a woman and four of her children, emergency services said.

Another 13 Palestinians died in other raids across Gaza throughout the day, they said.

But the strikes failed to staunch the rocket fire by Gaza militants, which sent Israelis scurrying into shelters across an ever broadening swathe of the country.

Two long-range rockets crashed into the sea off the northern port city of Haifa Wednesday, Israeli media reported, in an attack Hamas claimed.

Haifa lies 165 kilometres (100 miles) north of Gaza and, if confirmed, it would be the furthest a rocket fired from there has ever travelled.

Public radio said one struck near the seaside resort of Caesarea and another in the Carmel Beach region, both south of Haifa.

Another three were fired at the southern town of Dimona where Israel has a nuclear reactor, the military said on Twitter.

"Palestinian terrorists in Gaza fired three rockets at Dimona. Two fell in open areas; Iron Dome intercepted the other," it said, referring to the Israeli missile defence system.

The Ezzedine Al-Qassam Brigades, the military wing of the Gaza-based Hamas, said it "launched three M75 rockets at Dimona," referring to the Gaza-produced rockets with a range of about 80 kilometres (50 miles).

Army radio quoted a military source as saying Hamas had dozens of such rockets in its arsenal.

So far, neither side has shown any sign of backing down, as Israel stepped up its preparations for a possible ground assault, approving the call up of 40,000 reservists.

*This article was edited by Ahram Online