Magen Daviv Adom, Israel's national emergency medical services, said there were "dozens" killed, but did not offer specific numbers. It also said in a tweet that that 38 were critically inured and still at the location, six were in critical condition at a hospital, 18 were severely injured, two were moderately injured and 39 were lightly injured.
Video from the scene showed dozens of ambulances lined up for patients.
The Israeli military said it sent helicopters to aid in rescue efforts.
The MDA confirmed six helicopters were sent to work with ambulances to bring victims to Ziv Hospital in Safed and Galil Medical Center in Nahariya.
Lag BaOmer is an annual celebration on the anniversary of the death of Rabbi Shimon bar Yochai, who was buried in a tomb at Mount Meron in northern Israel. The festivities include pilgrimages to bar Yochai's tomb and lighting bonfires and celebrating throughout the night.
This is a developing story. Check back for updates.
ABC News' Bruno Nota, Christine Theodorou and Rashid Haddou contributed to this report.