At least 492 people have been killed in intense and wide-ranging Israeli air strikes targeting Hezbollah in Lebanon, the country’s health ministry says, in the deadliest day of conflict there in almost 20 years.

Thousands of families have also fled their homes as the Israeli military said it hit 1,300 Hezbollah targets in an operation to destroy infrastructure that the armed group had built up since the 2006 war.

Hezbollah, meanwhile, launched more than 200 rockets into northern Israel, according to the military. Paramedics said two people were injured by shrapnel.

World powers have been urging restraint as both sides appear to be spiralling closer towards all-out war.

Lebanon's health ministry said 35 children and 58 women were among the dead, while 1,645 others had been wounded.

It did not report how many of the casualties were civilians or combatants.

Health Minister Firass Abiad said thousands of families had also been displaced by the strikes.

UN Secretary General António Guterres expressed alarm at the escalating situation and said he did not want Lebanon to “become another Gaza”.

President Joe Biden said the US was “working to de-escalate in a way that allows people to return home safely”, while the Pentagon announced it was sending “a small number” of additional troops to the Middle East "out of an abundance of caution".

Nearly a year of cross-border fighting between Israel and Hezbollah sparked by the war in Gaza has killed hundreds of people, most of them Hezbollah fighters, and displaced tens of thousands on both sides of the frontier.

Hezbollah has said it is acting in support of Hamas and will not stop until there is a ceasefire in Gaza. Both groups are backed by Iran and proscribed as terrorist organisations by Israel, the UK and other countries.

The Pentagon said it was sending “a small number” of additional US troops to the Middle East amid the growing crisis.

"In light of increased tension in the Middle East and out of an abundance of caution, we are sending a small number of additional US military personnel forward to augment our forces that are already in the region," said Pentagon spokesman Maj Gen Pat Ryder in a briefing with reporters.

He would not answer any follow-up questions on the specifics.

Lebanese media said the first wave of Israeli air strikes began at around 06:30 local time (03:30 GMT) on Monday.

“It was horrifying, the missiles flew over our heads. We woke up to the sound of bombings, we didn’t expect this,” one woman said.

Dozens of towns, villages and open areas were targeted throughout the day in the districts of Sidon, Marjayoun, Nabatieh, Bint Jbeil, Tyre, Jezzine and Zahrani in southern Lebanon, as well as the Zahle, Baalbek and Hermel districts in the eastern Bekaa Valley, according to the state-run National News Agency (NNA).

In the evening, it reported that a building in the Bir al-Abed area of the southern suburbs of the capital, Beirut, was hit by several missiles.

Lebanese security sources said the strike targeted Hezbollah’s top commander in southern Lebanon, Ali Karaki, but that it was not clear whether he was killed. Hezbollah’s media office said Karaki was “fine” and had “moved to a safe place”.

From the south to Beirut, roads were congested as people desperately tried to leave amid the bombardment and after receiving audio and text messages from the Israeli military warning them to move away immediately from buildings where Hezbollah was storing weapons.

A family of four riding on a motorbike spoke to the BBC in Beirut during a brief stop on their way to the northern city of Tripoli. "What do you want us to say? We just had to flee," the father said anxiously.

Information Minister Ziad Makary said his ministry had received an Israeli phone call urging it to evacuate its building in Beirut. However, he insisted that it would not comply with what he called “a psychological war”.

Prime Minister Najib Mikati, meanwhile, told a cabinet meeting: “The continued Israeli aggression on Lebanon is a war of extermination in every sense of the word.”

“We are working as a government to stop this new Israeli war and to avoid descending into the unknown,” he added.

The Israel Defense Forces (IDF) said in a statement on Monday evening that its aircraft had carried out strikes on approximately 1,300 Hezbollah "terror targets" in southern Lebanon and the Bekaa Valley where it claimed that rockets, missiles, launchers, and drones were hidden.

“Essentially, we are targeting combat infrastructure that Hezbollah has been building for the past 20 years. This is very significant,” the IDF’s Chief of Staff, Lt Gen Herzi Halevi, told commanders in Tel Aviv.

“Ultimately, everything is focused on creating the conditions to return the residents of the north to their homes.”

IDF spokesman Rear Adm Daniel Hagari said videos from southern Lebanon showed "significant secondary explosions caused by Hezbollah’s weapons that were being stored inside the buildings".

"It is likely that some of the casualties are from these secondary explosions," he added.

Israeli Prime Minister Benjamin Netanyahu urged the people of Lebanon to “get out of harm's way now”.

“For too long, Hezbollah has been using you as human shields. It placed rockets in your living rooms and missiles in your garage,” he said. “To defend our people against Hezbollah strikes, we must take out these weapons.”

A senior Israeli military official insisted that the IDF was “currently focusing on Israel’s aerial campaign only” after being asked by reporters if a ground invasion of southern Lebanon was imminent to create a buffer zone.

The official said Israel had three aims - to degrade Hezbollah's ability to fire rockets and missiles over the Lebanon-Israel border, to push its fighters back from the frontier, and to destroy the infrastructure built by Hezbollah’s elite Radwan Force which could be used to attack Israeli communities.

Hezbollah did not comment on the Israeli claims that it had hidden weapons in houses, and its media office had announced the death of only one fighter by Monday evening.

But in a sign that it is unlikely to back down, it said it had responded to the “Israeli enemy’s attacks” by firing barrages of rockets at several Israeli military bases in northern Israel, as well as a weapons manufacturing facility in the coastal Zvulun area, north of the city of Haifa.

The IDF said 210 projectiles had crossed from Lebanon by the evening, and that an unspecified number had landed in the Lower Galilee and Upper Galilee regions, in Haifa and the nearby areas of Carmel, HaAmakim and Hamifratz areas, and in the occupied Golan Heights.

One house was badly damaged by a rocket in Givat Avni, in the Lower Galilee.

Resident David Yitzhak told the BBC that he, his wife and six-year-old daughter were unharmed because they had managed to get behind the solid door of the house's safe room seconds earlier, when a warning siren sounded.

“It’s a metre from life to death,” he said.

Israel’s ambulance service said it treated two people with shrapnel wounds in the Lower and Upper Galilee regions, and that another person was injured as they rushed to a shelter.

On Sunday, Hezbollah launched more than 150 rockets and drones across the border, while Israeli jets struck hundreds of targets across southern Lebanon.

Hezbollah remains a powerful force, despite being weakened by what Israel’s defence minister described as “the most difficult week” for the group since its establishment.

On Tuesday and Wednesday, 39 people were killed and thousands were wounded after thousands of pagers and walkie-talkies used by Hezbollah exploded. And on Friday, Hezbollah said at least 16 members, including top commanders of its elite Radwan Force, were among 45 people killed in an Israeli air strike in southern Beirut.

Speaking at a funeral on Sunday, Hezbollah's deputy leader Naim Qassem said the group would not be deterred.

"We have entered a new phase,” he said, “the title of which is the open-ended battle of reckoning."

On the streets of Beirut, one young man told the BBC that he was "very scared of the war escalating" because it would “ cause a lot of disaster, it will stop students going to university".

But another man was defiant, saying: "We're not scared, we have to stand tall, we have to defend ourselves."