Nearly 40 people were killed and hundreds of others injured when a stampede broke out overnight at an overcrowded Jewish religious gathering in Israel's north attended by tens of thousands of people flouting the coronavirus pandemic-related restrictions.

The mass gathering was organised to celebrate the Lag B'Omer, an annual religious holiday marked with all-night bonfires, prayer and dancing, at Mount Meron.

The town is the site of the tomb of Rabbi Shimon Bar Yochai, a second-century sage, and is considered to be one of the holiest sites in the Jewish world.

Israel recently eased mask-wearing requirements in open areas and other restrictions after the success of a massive vaccination drive that significantly brought down Coronavirus-related cases.

The resulting "normalcy", with limitations, saw rejoicing crowds across Israel on Thursday evening with youngsters, especially school children, coming out in large numbers in open spaces putting bonfires that accompanied the Lag BaOmer festivities.

Tens of thousands of ultra-orthodox Jews participated in the tragic event Thursday night at the tomb of Rabbi Shimon Bar Yochai, making it the largest event held in Israel since the coronavirus pandemic broke out last year.

A Magen David Adom (MDA) rescue service official confirmed that at least 38 people had been killed with the numbers likely to go even higher.

"Our paramedics have treated hundreds of people, including several in serious condition. All the wounded were evacuated to hospital", he said.

Some 150 people were injured in the accident.

MDA Director-General Eli Bin told the Ynet news site that the wounded were being evacuated to the Ziv hospital in Safed, the Galilee Medical Center in Nahariya, Rambam hospital in Haifa, Poriya hospital in Tiberias, and Hadassah Ein Kerem hospital in Jerusalem.

Firefighters worked to free the trapped, supported by Israeli Air Force helicopters and rescue services.

Police were trying to clear the tens of thousands who attended the event from the area.

A preliminary police investigation revealed that some of the attendees slipped on the stairs, creating a "human avalanche" that crushed members of the crowd.

At around midnight on Thursday, organisers had estimated that some 100,000 people were at the site, with an additional 100,000 expected to arrive by Friday morning, local media reported.

A police official told the local media that dozens of participants in a concert had “slipped,” falling on those below them while walking along a slippery walkway and causing a crushing domino effect.

Videos posted on social media showed chaotic scenes as Ultra-Orthodox men clambered through gaps in sheets of torn corrugated iron to escape the crush, as police and paramedics tried to reach the wounded.

Bodies lay on stretchers in a corridor, covered in foil blankets.

Health Ministry officials had urged Israelis not to travel to Mount Meron, worried the festivities could lead to mass coronavirus contagion, Times of Israel reported.

Since the site was so densely populated, search and rescue authorities say they struggled to evacuate trapped people.

"I had just sat down to eat when I heard the screams; We rushed to help, and then we saw the bodies," Avi, a witness who helped treat the injured told the Haaretz newspaper.

"It happened in a split second; people just fell, trampling each other. It was a disaster," another witness told the newspaper.

Some 5,000 police officers were said to have been deployed at the event.

Prime Minister Benjamin Netanyahu called it a "terrible disaster" requesting rescue authorities to bolster their presence at the scene.

President Reuven Rivlin also offered his condolences.

A Times of Israel report published before the tragic incident said that the government failed to reach an agreement on how to handle the celebrations, with Prime Minister Netanyahu reportedly wary of angering Haredi (ultra-orthodox Jews) political parties by imposing restrictions.

The ultra-orthodox parties have firmly stood behind Netanyahu during the political uncertainty that has gripped Israel over the last two years throwing four inconclusive elections.

Last year, the celebrations were severely curtailed over contagion fears.

"But police and health officials have instituted their own rules at the site to try to keep the pilgrims from congregating at close quarters for lengthy periods of time", the report had said.