
Police were investigating the cause of explosion at the site in Kelapa Gading, North Jakarta, city police chief Asep Edi Suheri told a televised press conference.
The number of people admitted to hospitals was 54, he said, adding the injuries ranged from minor to serious and included burns.
News channels KompasTV and MetroTV showed footage of a police line around the school with ambulances standing by. Images of the mosque showed no extensive damage.
Meanwhile, an eyewitness told KompasTV that two explosions were heard while he was in the mosque for Friday prayers.
The witness, who was in the front row of the congregation, said one of the explosions occurred inside the mosque and another outside, prompting the worshippers to flee in panic.