A fire tore through a prison in Banten on Wednesday, killing 41 people and injuring dozens of others, an official said.

The blaze at the Tangerang Penitentiary, just outside the capital Jakarta, broke out in the early hours when most inmates were asleep.

Rescue teams were able to put out the fire, which was mostly contained in one block that housed prisoners jailed over drug charges, at around 3:00 am (2000 GMT Tuesday) and evacuated the victims. 

"Forty-one inmates died, eight were badly injured and 72 others sustained minor injuries," Jakarta police chief Insp. Gen. Fadil Imran told a press conference.

Victims with serious injuries were rushed to Tangerang's general hospitals for treatment, while prisoners with minor wounds were treated in a health clinic.

Authorities are still investigating the cause of the incident, but suspected an electrical fault may be behind the fire.

"I have checked the scene, based on early observation, it is suspected (the fire) happened because of a short circuit," Fadil said, quoted by AFP.

Rika Aprianti, a spokeswoman of the Directorate General for Penitentiary in the Ministry of Law and Human Rights, said: "the cause is under investigation," she said, adding that the fire broke out at 1 to 2 a.m. on Wednesday.

She said that authorities were still evacuating the jail.

Rika later said as quoted by Kyodo News the prison block where the fire occurred had held 122 inmates, and that the prison "has been overcapacity."

The prison block housed those convicted in drug cases.

Overcrowding is a problem in most prisons in Indonesia.