The fire started early Wednesday morning, local time, in Block C of Tangerang Prison in Banten Province, according to Jakarta police spokesman Yusri Yunus.
Yusri said firefighters stopped the spread of the fire to other blocks of the prison and fought the flames for two hours before it was extinguished.
An investigation into the cause of the fire is ongoing, but Yusri said they initially suspect he has an electrical short circuit.
Rika Aprianti, spokeswoman for the prisons department of the ministry of human rights and human rights, said authorities were still evacuating the facility and “the cause is being investigated.”
The block housed inmates detained for drug-related offenses and had a capacity for 122 people, he said. He did not say how many people were present when the fire broke out, but confirmed that the prison was overcrowded.
The Tangerang prison, an industrial and manufacturing center near Jakarta, housed more than 2,000 inmates, a capacity well in excess of 600 people, according to government data in September.
Kompas TV showed footage of firefighters trying to put out huge flames from the top of a building. The station reported that 41 people were killed and eight seriously injured.
Indonesia’s Metro TV quoted a police report as saying that 73 people also had minor injuries.