Israeli tanks and troops are massing at the Gaza border amid speculation of a ground invasion and warning of potential ‘civil war’ as violence between Jews and Arabs spills onto Israeli streets.

Israel is mobilising more than 9000 reservist troops in what officials labelled an “exceptional call-up” after four days of escalating rocket attacks and air strikes between the military and Palestinian militants.

Israel was in “various stages of preparing ground operations”, a military spokesman said.

Hamas armed wing spokesman Abu Ubaida responded to the troop build-up with defiance, urging Palestinians to rise up.

“Mass up as you wish, from the sea, land and sky. We have prepared for your kinds of deaths that would make you curse yourselves,” he said.

The violence has touched off clashes and riots in Israel’s cities where mixed communities of Jews and Arabs who had been living alongside one another became a new front in the conflict.

In the fighting inside Israel, where some in the 21 per cent Arab minority have mounted violent pro-Palestinian protests, attacks by Jews on Arabs passing by in ethnically mixed areas have worsened.

Israeli President Reuven Rivlin called for an end to “this madness” and warned of civil war in the country.

“We are endangered by rockets that are being launched at our citizens and streets, and we are busying ourselves with a senseless civil war among ourselves,” said the president, whose role is largely ceremonial.

Israeli Arabs outside a mosque during clashes between Jews, Israeli police and Arabs, in the mixed town of Lod, central Israel. Photo: AAP

It comes as Israeli Prime Minister Benjamin Netanyahu said the campaign “will take more time”.

Worried that the region’s worst hostilities since 2014 which flared up Monday could spiral out of control, the United States is sending an envoy, Hady Amr.

In renewed air strikes on Gaza, Israel struck a six-storey residential building in Gaza City that it said belonged to Hamas, the Islamist group that controls the Palestinian enclave.

Palestinian militants have fired more rockets into Israel’s commercial heartland as Israel kept up a punishing bombing campaign.

It’s now being reported 100 people have been killed in Gaza, and Gaza’s health ministry earlier said the dead included 18 children and eight women.

Seven people have been killed in Israel, its military said.

Mr Netanyahu said Israel has struck close to a thousand militant targets in Gaza in total.

Palestinian people inspecting their destroyed houses after an Israeli air strike in Beit Lahia northern Gaza strip. Photo: AAP

US President Joe Biden said he hoped fighting “will be closing down sooner than later”.

But Mr Netanyahu has vowed to “continue acting to strike at the military capabilities of Hamas” and other Gaza groups. Hamas is regarded as a terrorist group by the United States and Israel.

A tower building is destroyed by Israeli air strikes in Gaza City. Photo: AAP

Israel launched its offensive after Hamas fired rockets at Jerusalem and Tel Aviv in retaliation for Israeli police clashes with Palestinians near al-Aqsa mosque in East Jerusalem during the Muslim fasting month of Ramadan.

The fatalities in Israel include a soldier killed while patrolling the Gaza border and six civilians, including two children and an Indian worker, medical authorities said.

Meanwhile British Airways, Virgin Atlantic and Iberia have all cancelled flights to Tel Aviv as European carriers joined US airlines in avoiding flying to Israel.

Virgin Atlantic had said earlier this week that bookings to Israel had soared 250 per cent week on week after an announcement by Britain that Israel was on its “green list” for the reopening of overseas leisure travel during the COVID-19 pandemic.

But an explosion of violence, with fighting in Jerusalem and the Gaza Strip causing mounting civilian deaths, have made international airlines wary of the region.

-with AAP