"I know that the citizens of Israel are on alert, and I ask of you one thing - keep patient and cool," Prime Minister Benjamin Netanyahu said on Wednesday while meeting new army recruits.

"We are prepared for both defence and attack, we are striking our enemies and are also determined to defend ourselves."

Israel now finds itself facing the threat of a multi-front war, confronting a clutch of militant movements - Hamas, Hezbollah, the Houthis in Yemen, all backed and funded by its longstanding enemy Iran.

An attack is expected in the coming days following vows from Iran and Hezbollah to retaliate for the assassinations last week of Hamas leader Ismail Haniyeh in Tehran and Hezbollah military commander Fuad Shukr in Beirut.

After months of alarm and an attack by hundreds of Iranian missiles in April that was thwarted by Israel's air defences and the help of international allies, Israelis have become used to the crisis.

Tens of thousands of people were evacuated from northern areas in range of Hezbollah rockets at the start of the war and many border areas now have a ghostly, abandoned air.

But a prolonged bombardment from Hezbollah's rocket arsenal could reach deeper into the country to sensitive targets like the port city of Haifa in northern Israel, which is well in range.

The city's Rambam Hospital has been on alert since last October and has readied its three-floor, fortified underground facility to treat patients.

"We're waiting to see what happens," said David Ratner, a hospital spokesperson.

The military is on high alert and last weekend it augmented its nationwide system of air raid sirens and broadcast alerts to include real-time text messages to be sent to residents in targeted areas.

Many local councils have advised residents to reduce non-essential activity, stay near protected areas and avoid large gatherings.

In Haifa, public bomb shelters have been equipped with digital systems so they can be unlocked remotely during an attack, said Yair Zilberman, director of the city's security and emergency services department. They are also being equipped with generators.

A number of underground parking lots have been approved as makeshift shelters with enough space for thousands of residents if needed, Zilberman said.

In the city of Ramla in central Israel, national ambulance service Magen David Adom (MDA) has been collecting blood donations in a subterranean service centre, shielded with extra-thick concrete walls, blast doors and airlocks.

"We've got the threats from Iran, we've got threats from Hezbollah," said MDA's Aryeh Myers. 

"Massive rocket attacks, massive threats to the state of Israel and we want to make sure that we are ready for anything."

Last Thursday, the Environmental Protection Ministry held a situational assessment to decide how best to protect factories with inventories that could be dangerous if targeted in a missile strike, or how to deal with an attack on a building that contains asbestos.

The military said the Home Front Command keeps in constant contact with factories and local authorities to maintain a "complete picture of the inventory levels of hazardous materials".

The Bazan Group, which operates in Haifa one of the largest oil refineries in the eastern Mediterranean, told Reuters it was "working to maintain energy security and the continuity of fuel supply to the economy."

Mass cash withdrawals are another scenario for which authorities are preparing.

"The stock of banknotes and coins in the Bank of Israel and the banking system will, according to every visible forecast, be sufficient," the Bank of Israel said.

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