Israeli warplanes have pounded Gaza relentlessly, causing a growing number of civilian casualties, as the UN Security Council is to meet urgently over Israel’s spiralling confrontation with Hamas.

Palestinian president Mahmud Abbas has accused Israel on Thursday of committing “genocide” in Gaza, but Israel showed no sign of letting up, with five children among 22 Palestinians killed in air strikes carried out since midnight local time.

And Israeli Prime Minister Benjamin Netanyahu has vowed even tougher action against Hamas, despite growing international calls for a cease-fire in the worst confrontation in and around Gaza since 2012.

So far, there have been no Israel deaths but Hamas has kept up a steady barrage of rocket fire on cities in central Israel, sending people fleeing for cover as air raid sirens rang out in cities as far away as Jerusalem, Tel Aviv and even Haifa.

The violence has emptied the streets from Gaza City to Tel Aviv, as both Israelis and Palestinians take shelter indoors for fear of being caught in the open when the next rocket or missile hits.

On the beachfront in Tel Aviv, cafes which would normally have been bursting at the seams at the height of tourist season, sat empty, their waiters nervously checking the phones for any news of an incoming missile.

But in cafes in Gaza, the story was much darker after an Israeli missile slammed into a coffee shop in Khan Yunis, killing eight as they watched a World Cup semi-final match. Another 15 people were injured.

And Israel has confirmed preparations are under way for a possible ground attack, with tanks seen massing along the border and Netanyahu facing mounting pressure from hardliners within his coalition to put boots back on the ground in the territory from which Israel pulled all troops and settlers in 2005.

“If the fire continues, we do not rule out a ground incursion,” President Shimon Peres told CNN on Wednesday, warning it could happen “quite soon”.

A Palestinian man crosses the street in the aftermath of an Israeli airstrike.

“Gaza is on a knife edge. The deteriorating situation is leading to a downward spiral which could quickly get beyond anyone’s control,” UN chief Ban Ki-moon warned ahead of an emergency meeting of the Security Council.

“The risk of violence expanding further still is real. Gaza, and the region as a whole, cannot afford another full-blown war,” he said.

Ban spoke with Netanyahu, urging him to exercise maximum restraint, although he described the Gaza rocket attacks as “unacceptable and must stop”.

He also spoke with Abbas, Egypt’s President Abdel Fattah al-Sisi and US Secretary of State John Kerry over the crisis, which drawn calls for restraint from Washington and the European Union.

As the number of victims in Gaza rose, Egypt opened the Rafah border crossing, with hospitals in north Sinai placed on stand-by to receive the wounded, Egypt’s official MENA news agency reported.

Five children and four women were among 22 people killed in Israeli air strikes on Thursday, medics said, with most of the bloodshed in Khan Yunis.

The deaths bring to 73 the overall number of Gazans killed since Israel launched Operation Protective Edge early on Tuesday to halt cross-border rocket fire.