Israel launched airstrikes on Beirut's southern suburbs and other areas of Lebanon on Saturday, a day after carrying out a massive attack on Hezbollah's headquarters that appeared to be aimed at killing its leader, Sayyed Hassan Nasrallah.

The fate of Nasrallah, leader of the Iran-backed group for 32 years, remains unclear, with Hezbollah yet to issue any statement on his status.

Reuters journalists heard more than 20 airstrikes in Beirut before dawn on Saturday and more after sunrise. Smoke could be seen rising over the city's Hezbollah-controlled southern suburbs, known as the Dahiyeh.

Thousands of people have fled the area since Friday's attack, congregating in squares, parks and sidewalks in downtown Beirut and seaside areas.

"They want to destroy Dahiyeh, they want to destroy all of us," said Sari, a man in his 30s who gave only his first name, referring to the suburb he had fled after an Israeli evacuation order. Nearby, the newly displaced in Beirut's Martyrs Square rolled mats onto the ground to try to sleep.

The Israeli military said a missile fired at central Israel on Saturday had struck an open area. Earlier, the military said about 10 projectiles had crossed from Lebanon into Israeli territory and that some had been intercepted.

The Israeli military also said it was striking Hezbollah targets in the Bekaa Valley, a region of eastern Lebanon at the Syrian border that it has pounded over the last week.

Israel's five hours of continuous strikes on Beirut early on Saturday followed Friday's attack, by far the most powerful by Israel on the city during the conflict with Hezbollah that has played out in parallel to the Gaza war for nearly a year.

The escalation has sharply increased fears the conflict could spiral out of control, potentially drawing in Iran, Hezbollah's principal backer, as well as the United States.

There was no immediate confirmation of Nasrallah's fate after Friday's heavy strikes, but a source close to Hezbollah told Reuters he was not reachable.

Israel has not said whether it tried to hit Nasrallah, but a senior Israeli official said top Hezbollah commanders were targeted.

"I think it's too early to say... Sometimes they hide the fact when we succeed," the Israeli official told reporters when asked if the strike on Friday had killed Nasrallah.

Earlier, a source close to Hezbollah told Reuters that Nasrallah was alive.

Iran's Tasnim news agency also reported he was safe. A senior Iranian security official told Reuters that Tehran was checking his status.

The Israeli military said in a statement that it had killed the commander of Hezbollah's missile unit, Muhammad Ali Ismail, and his deputy Hossein Ahmed Ismail.

Israel's attacks in Lebanon have widened to new areas this week. On Saturday, an airstrike hit the Lebanese mountain town of Bhamdoun, southeast of Beirut, Lebanese lawmaker for the area Mark Daou told Reuters.

The mayor of Bhamdoun, Walid Khayrallah, told Reuters the strike hit a large empty lot and did not cause any casualties.

Hours before the latest barrage, Israeli Prime Minister Benjamin Netanyahu told the United Nations that his country had a right to continue the campaign.

"As long as Hezbollah chooses the path of war, Israel has no choice, and Israel has every right to remove this threat and return our citizens to their homes safely," he said.

Several delegations walked out as Netanyahu approached the lectern. He later cut short his New York trip to return to Israel.

Lebanese health authorities confirmed six dead and 91 wounded in the initial attack on Friday - the fourth on Beirut's Hezbollah-controlled southern suburbs in a week and the heaviest since a 2006 war.

The toll appeared likely to rise much higher. There was no word on casualties from the later strikes. More than 700 people were killed in strikes over the past week, authorities said.

Hezbollah's al-Manar television reported seven buildings were destroyed.

Hours later, the Israeli military told residents in parts of Beirut's southern suburbs to evacuate as it targeted missile launchers and weapons storage sites it said were under civilian housing.

Hezbollah denied any weapons or arms depots were located in buildings that were hit in the Beirut suburbs, the group's media office said in a statement.

Alaa al-Din Saeed, a resident of a neighbourhood that Israel identified as a target, told Reuters he was fleeing with his wife and three children.

"We found out on the television. There was a huge commotion in the neighbourhood," he said. The family grabbed clothes, identification papers and some cash but were stuck in traffic with others trying to flee.

"We're going to the mountains. We'll see how to spend the night - and tomorrow we'll see what we can do."

Around 100,000 people in Lebanon have been displaced this week, increasing the number uprooted in the country to well over 200,000.

Israel's government has said that returning some 70,000 Israeli evacuees to their homes is a war aim.

Hezbollah has fired hundreds of rockets and missiles against targets in Israel, including Tel Aviv. The group said it fired rockets on Friday at the northern Israeli city of Safed, where a woman was treated for minor injuries.

Israel's air defence systems have ensured the damage has so far been minimal.

Iran, which said Friday's attack crossed "red lines", accused Israel of using U.S.-made "bunker-busting" bombs.

At the U.N., where the annual General Assembly met this week, the intensification prompted expressions of concern including by France, which with the U.S. has proposed a 21-day ceasefire.

U.S. Secretary of State Antony Blinken told a New York press conference: "We believe the way forward is through diplomacy, not conflict... We will continue to work intentionally with all parties to urge them to choose that course."

Hezbollah opened the latest bout in a decades-long conflict with a missile barrage against Israel immediately following the Oct. 7 attack on Israel by the Palestinian militant group Hamas in Gaza last year.