Dozens of people have been rushed to hospital after an explosion at a mosque in the Indonesian capital Jakarta, local police said.

The incident happened during Friday prayers inside a school complex in Kelapa Gading, North Jakarta.

City police chief Asep Edi Suheri said the cause of the explosion is still being investigated. Witnesses reported hearing two loud blasts around midday (04:00 GMT), just as the sermon had started at the mosque.

Fifty-four people, mostly students, have been admitted to hospital with injuries ranging from minor to serious and including burns, Suheri said. Twenty remain in hospital care, with three suffering from serious injuries, he added.

Suheri said an anti-bomb squad that was deployed at the scene found toy rifles and a toy gun near to the mosque.

“Police are still investigating the scene to determine the cause of the blasts,” he explained.

Local news channels showed footage of a police line around the school with ambulances standing by. Images of the mosque showed no extensive damage.