Dozens more were hurt at the Lag B'Omer event in northern Mount Meron, where annual commemorations included all-night prayer and dancing.

Chaotic scenes were captured on social media, showing men clambering through gaps in sheets of torn corrugated iron as they tried to escape the crush in the early hours of the morning.

"Masses of people were pushed into the same corner and a vortex was created," witness Dvir told Army Radio. "I felt like I was about to die."

Attendee Shlomo Katz said: "We were standing and waiting for our friends - we were going to go inside for the dancing - and all of a sudden we saw paramedics running by, mid-CPR on kids."

Ambulances then began arriving "one after the other", he added.

Paramedic Omri Giorga said he saw "tens of people lying on the floor" and "tens of injured, walking and bleeding".

A man called Yitzhak told Channel 12 TV: "We thought maybe there was a (bomb) alert over a suspicious package.

"No one imagined that this could happen here. Rejoicing became mourning; a great light became a deep darkness."

Six people are in a critical condition after 150 were taken to hospital, said Zaki Heller, a spokesman for the Magen David Adom ambulance service.

"In one moment, we went from a happy event to an immense tragedy," he added.

Photographs show rows of wrapped bodies lying on the ground and dozens of ambulances.

Mobile intensive care units and helicopters were used to transport the most seriously injured to hospital.

"Close to 200 life-saving vehicles" were sent to the scene, emergency services spokesman Yoni Yagodozsky told Sky News, in addition to the "huge fleet" already there.

Mr Yagodozsky said the tragedy, which took place in a hilly area, happened while "people were on their way down from the main ceremony".

The path was narrow and "people tripped over", while those behind "simply walked on them and that's what created this horrible, horrible incident", he said.

Channel 13 TV showed photographs of seven boys and teenagers who may be missing.

Mr Yagodozsky said first responders are "well trained and well prepared" for these types of events, and had actually completed an exercise anticipating such a scenario.

"In the beginning, there was concern that one of the construction sets built in the area had collapsed. Then, it became more and more clear that people were trying to escape," he said.

There will be a "thorough investigation" following the "huge tragedy", Mr Yagodozsky added.

Funerals are expected to happen today.

Police shut the site down and ordered attendees to be evacuated by bus.

Prime Minister Benjamin Netanyahu described the incident as a "heavy disaster", adding: "We are all praying for the wellbeing of the casualties."

It is one of the country's deadliest civilian events.

Emergency services deal with casualties  IMAGE: Sky News

About 100,000 ultra-Orthodox Jews had gathered at the tomb of second-century sage Rabbi Shimon Bar Yochai, considered one of the holiest sites in the Jewish world.

It was the first large-scale religious festival held since almost all Israel's coronavirus restrictions were lifted. In previous years, up to a quarter of a million people have gathered.

The site is mostly gender-segregated and mobile-phone video suggests the crush took place mainly in the men's areas.

The gathering had been held despite health officials warning that crowding could cause COVID-19 to spread.

Israel has seen cases plummet since launching one of the world's most successful vaccination campaigns late last year.

More than 54% of the population has been fully vaccinated.

Sky News/Andy Hayes