JAKARTA, Aug. 18 (Xinhua) -- Around 25 to 30 inmates escaped from a crowded prison in Indonesia's northern Sumatra Island on Sunday afternoon after a riot, local media reported.

The inmates at the Labuhan Ruku prison in Batubara Regency, 120 km southeast of North Sumatra Province's capital city Medan, broke through the security post, attacked the guards and burned the prison's registration room at 17:00 Jakarta time.

Akbar Hari, penitentiary affairs spokesman at the Indonesia's justice ministry told Indonesia's news portal detik.com that the inmates leaped over the wall at the back of the prison following the fire, adding that the authority is trying to regain control of the prison.

With a capacity to accommodate only 300 inmates, now a total of 867 prisoners were jailed there, according to Hari.

Hari said the prison is calculating the exact number of the escaped inmates and a probe has been launched into the riot. Hari added that police officers and the army personnel are deployed around and in the prison.

Indonesia's prisons are often criticized for poor security and overcrowdedness. Last month around 200 inmates escaped from a overcrowded prison in Medan's Tanjung Gusta prison following a similar riot.