Multiple explosions occurred during Friday prayers at a mosque inside a high school in Indonesia’s capital, Jakarta, injuring at least 55 people, most of them students, police said.

Witnesses reported hearing at least two blasts, both inside and outside the mosque at SMA 27 — a state high school within a navy compound in northern Jakarta’s Kelapa Gading area — just as the sermon began. Students and others ran in panic as gray smoke filled the mosque.

Jakarta Police Chief Asep Edi Suheri said the explosions appeared to have originated near the mosque’s loudspeaker, though the cause has not yet been determined. Most victims sustained cuts, burns, and injuries from flying glass.

Emergency teams took the injured to nearby hospitals, where 20 students remain hospitalized with burns, including three in serious condition. Others were released after initial treatment.

Videos circulating online showed students in uniform running across the school courtyard, covering their ears against the noise, while some of the injured were carried on stretchers to waiting vehicles.

Parents gathered at Yarsi and Cempaka Putih hospitals seeking information about their children. Some said their children had injuries caused by nails and fragments from the explosion.

Police found toy rifles and a toy gun near the scene, Suheri said, adding that an anti-bomb squad is investigating. “We ask the public not to speculate until the investigation is complete,” he told reporters.

Indonesia, the world’s largest Muslim-majority nation, has experienced several militant attacks in past decades, including the 2002 Bali bombings that killed 202 people. However, authorities say the country has seen a “zero attack” period since 2023 due to tightened security and counterterrorism measures.