(JTA) — Up to 30 people were injured in the Stamford Hill neighborhood of London after an explosion in a Lag b’Omer bonfire.

A fireball erupted when the bonfire was lit on Wednesday night. It initially was believed that smartphones placed on the bonfire were the cause of the blast. But it later was thought to be fuel placed on the wood to make it catch fire easier.

People at the bonfire “shrieked and panicked,” and others “trampled on one another,” according to the Yeshiva World News website, which published a video and photos of the incident.

Some 10 people were taken to the hospital with burns on their faces.

The rabbi of the community hosting the bonfire had spoken prior to lighting it about the dangers of smartphones and said he would be burning one, similar to a speech he had given the previous year, according to Yeshiva World News, which cited eye-witnesses to the bonfire. Other people reportedly also put their phones on the bonfire pile.

Lag b’Omer marks the 33rd day of the counting of the days between the holidays of Passover and Shavuot and the end of a minor mourning period recognizing the deaths of thousands of students of the second-century C.E. sage Rabbi Akiva. Lag b’Omer also commemorates the death Jewish kabbalist and mystic Rabbi Shimon Bar Yochai, a disciple of Akiva. The bonfires, lit at sundown, are meant to symbolize the light of his teachings.