The succesive strikes shook Beirut and its surroundings a little before 6:30 pm (15:30 GMT), leaving panicked residents scrambling for safety.
"I felt like the building was going to collapse on top of me, as if a rocket was going to hit me and kill me," said Abeer Hammoud, who lives in Beirut's southern suburbs.
"When it was over, I breathed a sigh of relief. It was as if I had been given a new lease of life," said the teacher in her 40s, still reeling from the shock.
The strikes killed at least two people and injured 76, Lebanon's health ministry said in a preliminary toll.
AFP footage showed several clouds of thick grey and pink smoke rising from the Haret Hreik area of the southern suburbs.
The Israeli army said it carried out "a precise strike" on Hezbollah's "headquarters", which Israeli media said targeted group chief Hassan Nasrallah -- stirring panic among Lebanese fearful of a wider escalation after nearly a year of near-daily exchanges that had been largely restricted to the border area.
A source close to Hezbollah told AFP that Nasrallah was "fine", but the group has issued no official statement.
Children rescued alive
The strikes left craters up to five-metre (16-feet) wide in Haret Hreik, an AFP photographer said, adding that ambulances were coming from all sides while fires burned.
Firefighters battled the blaze while rescuers rushed to find survivors amid the rubble, some using excavators.
Lebanon's official National News Agency reported two children had been pulled out from under the wreckage alive.
Lawyer Houssam al-Jawad, 45, who lives close to the targeted area said the explosions "lasted several seconds and sounded deep and strong, as if it were a successive series of sonic booms".
The windows and doors in the house shook even though it was located two kilometres (1.2 miles) from the site of the strike, he said.
The AFP photographer saw people rushing to the outskirts of the southern suburbs carrying clothes and suitcases.
Ahmad Ahmad, in his 60s, said he fled his house in the area after the strikes which felt "like an earthquake".
"I saw a strange mass of fire that shook houses around us," Ahmad said, strolling around the busy Hamra street, adding that he felt "exhausted".
This week Israel dramatically intensified its attacks, mostly on Hezbollah's south Beirut and southern and eastern Lebanese strongholds, killing more than 700 people, according to the health ministry.
UN special coordinator for Lebanon Jeanine Hennis-Plasschaert said in a statement on X that she was "profoundly worried about the potential civilian impact" of the "massive strikes".
"The city is still shaking with fear," she said.
