The Israeli military has ordered hundreds of thousands of people to leave Beirut's southern suburbs, a stronghold of Hezbollah, as it steps up strikes targeting the Iran-backed armed group across Lebanon.

"Save your lives, evacuate your homes immediately," the military's Arabic spokesperson wrote on X, apparently signalling plans for intense bombardment.

Huge traffic jams formed on main roads heading north and south as panicked residents complied with the unprecedented blanket order covering the area.

On Wednesday, the military told all residents of a huge swathe of southern Lebanon near the Israeli border to leave ahead of a much-anticipated ground incursion.

Mohammed al-Khaouzam was among those stuck in traffic trying to flee Beirut's southern suburbs on Thursday afternoon.