The UN human rights chief on Tuesday called on anyone with influence in the Middle East or elsewhere to seek to avert any further escalation in hostilities between Israel and Hezbollah, voicing alarm at the sharp escalation.

Israel's military said on Tuesday it struck dozens of Hezbollah targets in southern Lebanon overnight, a day after it launched a wave of airstrikes against the Iran-backed group's sites in Lebanon's deadliest day in decades. Nearly 500 people have been killed and tens of thousands have fled from areas of southern Lebanon.

"UN High Commissioner Volker Türk calls on all States and actors with influence in the region and beyond to avert further escalation and do everything they can to ensure full respect for international law," Ravina Shamdasani, the spokesperson for Turk said at a Geneva press briefing.

"The methods and means of warfare that are being used raises very serious concerns about whether this is compliant with international humanitarian law," she added.

Asked about reports that Israel had warned people through phone messages ahead of the strikes, she said: "Whether you've sent out a warning you're telling civilians to flee, doesn't make it OK to then strike those areas, knowing full well that the impact on civilians will be huge..."

At the same press briefing, Abdinasir Abubakar, aWHO official in Lebanon, said that some hospitals in the country were "overwhelmed" by the thousands of wounded people arriving. Four healthcare workers had been killed on Monday, he added.

"We have some evidence, and we have some documentation that shows that at least there were some attacks on health facilities, even the ambulances as well," he told the briefing, condemning the impact on Lebanon's fragile health sector.

The UN refugee agency's spokesperson Matthew Saltmarsh said more people are expected to flee their homes and that the agency is seeking to identify new shelters for displaced people around Beirut and the Bekaa valley.

"We're looking at tens of thousands (of displaced), but we expect that those figures will start to rise," he said. "The situation is extremely alarming. It's very chaotic, and we are doing what we can to support government."