Chadi Fares sits on the sidewalk of a Beirut street, watching emergency workers pick their way through piles of twisted metal and slabs of collapsed concrete.

The men are searching through the ruins of a residential building in Lebanon's capital for any survivors of last week's deadly Israeli bombing that killed at least 50 people.

Mr Fares's mother, father, grandfather, sister-in-law and five nieces and nephews were inside the building, in a second-storey apartment, when the Israeli air strike hit.

Some of their bodies are yet to be found.

"Everything is gone," he says, with tears in his eyes.

"Maybe sometimes we lie to ourselves and say maybe they are alive … but I don't think so.

"I don't know if angry is the word, there's no word."

Israel says it struck the building to target a meeting of senior Hezbollah commanders and claims it killed 16 of the militant group's operatives.

Lebanon's Ministry of Health says many civilians, including women and children, were also killed.

The bombing is the single deadliest attack Israel has launched on Hezbollah in almost a year of conflict between the two.

Mr Fares can't understand why his family has been dragged into a fight it had nothing to do with.

"Our enemy is not human, our enemy is a monster," he says, as he watches more bodies being pulled from the rubble.

Just days before the bombing, Israel launched a different attack inside Lebanon, that caused thousands of Hezbollah pagers and walkie-talkies to explode and killed more than 30 people.

The succession of events signalled a sharp escalation in the conflict between Israel and the militant group.

Hezbollah has now vowed significant retaliation against Israel, with the group's deputy leader Naim Qassem declaring his fighters are ready to face "all military scenarios".

"We've entered a new phase, titled, 'Open-ended battle of reckoning,'" he said at a funeral for some of the Hezbollah operatives killed in the building blast.

On Sunday Hezbollah followed through with the first phase of its threat by launching a barrage of more than 100 missiles deep into Israeli territory, and hitting areas that hadn't previously been Hezbollah targets.

One of the missiles fell in the middle of a residential street in the Israeli city of Kiryat Bialik, about 50 kilometres from the border with Lebanon.

Videos taken by witnesses from just after the impact show houses in the area ablaze, and walls demolished by shrapnel.

Three people were injured.

Rivka Vainer, 58, had only moved into her house, about 20 metres from the impact site, two days ago.

Now she's trying to clean up smashed windows, crumbling walls and a destroyed car.

"It was a big boom, and (now) all of the house is almost gone. It's two floors, and we have damage on both floors," she said.

"The situation is very weird for us because we all the time see the [conflict on] television from far … and now we are [in it]."

Warfare between Israel and Hezbollah has been largely contained to cross-border skirmishes since Hezbollah opened a new front with Israel about a year ago in support of Palestinians in Gaza.

Israel has now also threatened it is prepared to step up its military attacks inside Lebanon, fuelling concern that both sides appear to be spiralling closer toward all-out war.

Israel's Chief of the General Staff Herzi Halevi said the military was well-prepared for the next stages of fighting, which were coming in the next few days, but did not say what this would entail.

"We will do whatever it takes to remove threats against Israel," he said in a televised statement.

Mrs Vainer is adamant she doesn't want more fighting — and worries what will happen to her, and the rest of her country, should a wider war break out.

"All my stomach is turning around, I'm very scared of what happened," she said.

"I don't know what to do with my home. I don't know what to do with myself, because I'm very, very scared. I don't know what to do."