Dozens of people have been injured in an explosion during Friday prayers at a mosque inside a high school complex in Indonesia's capital, Jakarta.

Fifty-four people were admitted to hospital, city police chief Asep Edi Suheri told a televised news conference, with the injuries ranging from minor to serious and including burns.

Authorities said three people had suffered serious injuries and 17 others came away with minor injuries. Others have been treated and discharged, local media reports.

The Jakarta Metropolitan Police is now investigating the cause of the explosion at the site in Kelapa Gading, a district in North Jakarta, with a bomb disposal team deployed to the search area.

Images from the scene show bystanders watching as military personnel cordon off the entrance to the state-run high school complex. The explosion occurred around 12:15 local time (05:15 GMT), according to local reports.

A high-ranking Jakarta Metropolitan Police officer confirmed the presence of two objects resembling firearms at the scene. Images from Indonesia's government-owned news agency Antara suggest one of the objects appeared to be a submachine gun and another looked like a pistol.

The submachine gun-type object appears to be inscribed with: 14 words. For Agartha. On its body, it reads: Brenton Tarrant. Welcome to Hell. Brenton Tarrant is known for his mass shooting at a mosque in Christchurch, New Zealand in 2019.

A minister who visited the site later sought to dispel suggestions that real weapons were present, stating the objects were toys and calling for caution regarding any presumption of the explosion being a terrorist act as investigations continue.

Another object found was a dark green belt for storing gun cartridges. A pupil has claimed that a homemade bomb might have been brought by a student who had been bullied. Indonesia has the world’s largest Muslim population.