Violent explosions rocked the Haret Hreik neighbourhood in the Dahiyeh southern suburb of Beirut on Friday as the Israeli media reported the attack had targeted Hezbollah chief Hassan Nasrallah.
Ten loud explosions were heard in a wave of air raids that hit an area close to the road leading to Lebanon's only international airport in Beirut, with local media reporting that a large crater was seen on the site of the attack and that several buildings were flattened.
Footage aired on local media showed a massive column of smoke rising from the site of the strikes, described as "unprecedented".
It is expected that there will be a significant number of casualties resulting from the attack - but official figures are yet to be announced.
Local media cited a source close to Hezbollah as saying Nasrallah was alive and "doing well", without elaborating.
Israeli media reported that the military was unable to confirm whether Nasrallah was present at the site of the attack.
Earlier, Israeli military spokesperson Daniel Hagari gave a televised statement, saying his forces "carried out a precise strike on the central headquarters of the terrorist organisation Hezbollah in Dahiyeh".
The headquarters "served as the epicentre of Hezbollah's terror", he alleged.
The attack came soon after Israeli Prime Minister Benjamin Netanyahu gave a UN address in which he vowed to continue targeting Hezbollah in Lebanon.
Since Monday, Israel's attacks on Lebanon have killed over 700 people and wounded more than 6,000 more in what has been described as one of the highest death tolls within a week in modern wars.
"We will continue degrading Hezbollah until all our objectives are met," he told world leaders at the UN.
The headquarters is "located under residential buildings in the heart of Dahiyeh in Beirut," Rear Admiral Hagari said.