Defence Minister Israel Katz declared a state of emergency across the country, warning the public of Iranian missile and drone attacks.
The military ordered the public to follow emergency guidance as it announced tens of thousands of reservists were being called up for service, including to reinforce its land borders.
The police urged against non-essential travel to allow security and emergency vehicles to move freely.
Protected by a sophisticated air defence system, some Israelis went to the beach in Tel Aviv on Saturday ahead of the initial Iranian response, saying they felt safe and voicing support for an operation against Iran.
"It's about time," said Shira Dorany as she took a walk along Tel Aviv's Mediterranean-front promenade.
"I don't want to wait anymore for what's coming. Now, it's coming. Let's finish it."
There were a few reports of damage or injuries from Iran's initial missile barrages.
Israelis generally have access to bomb shelters and are warned to rush to them by a nationwide alert system.
Israel and Iran last year faced off in an aerial war, after Israel launched a surprise attack on Iran in June that the United States later joined.
The war lasted 12 days, killing over 30 people in Israel and more than 900 in Iran.
Tel Aviv, where several military sites are located, suffered multiple strikes during last year's war, as did parts of southern Israel where there are some military bases.
Israel on Saturday closed its airspace to civilian flights, although land borders with Egypt and Jordan remained open, according to a spokesperson from the airport authority.
The US Embassy in Jerusalem said government personnel had been advised to shelter in place, after on Friday that they should leave the country if they wished to.
In Jerusalem, people were seen rushing to buy food and withdraw money as explosions from missile interceptions echoed across the city.
At the Sheba Medical Centre near Tel Aviv, medical workers were moving entire hospital wards underground.
"(Sheba) switched to advanced preparedness mode in preparation for the strike in Iran. We are in the process of moving all our departments and services into protected areas," said Itai Pessach, the medical centre's director general.
At the beach in Tel Aviv, Maayan Eliasi, 43, said Israeli strikes on Iran were necessary "to establish that we are strong".
"We are not scared, and we are here to protect our land."
