Lebanon was drawn into the Middle East war last week when Hezbollah attacked Israel in response to the killing of Iranian supreme leader Ayatollah Ali Khamenei in US-Israeli strikes.

Israel expanded its strikes in Lebanon on Friday, targeting multiple areas, while Hezbollah also launched fresh attacks against Israeli forces.

"Israel's evacuation orders have now engulfed 1,470 square kilometres (some 570 square miles), or 14 percent of Lebanon, including south Lebanon, Beirut's southern suburb, and parts of Bekaa," the international NGO said.

More than 800,000 people in Lebanon are registered as displaced, according to local authorities, with nearly 130,000 people currently sleeping in official shelters.

"The massive displacement we have seen here is unique" in the ongoing Middle East war, World Food Programme Deputy Executive Director Carl Skau told AFP on Thursday, from Beirut.

"I mean (they) registered some 800,000 people in a week. That's massive."

Israel expanded its evacuation warnings for southern Lebanon on Thursday, telling people to head north of a river more than 40 kilometres (25 miles) above its border with Lebanon.

It had previously repeatedly told people south of the Litani River, about 30 kilometres from the southern border, to leave.

Israel has also issued evacuation warnings for most of Beirut's southern suburbs and parts of the eastern Bekaa valley.

The evacuation orders encompass most of the Shia-majority regions of Lebanon.

Hezbollah draws most of its support from the Shia community in religiously-diverse Lebanon, and most of its facilities are located in those regions.