Deputy Superintendent of Police of the area Wajid Thaheem told the media that the bus was engulfed in the fire when it reached the Nooriabad area of Jamshoror district of Sindh province, Xinhua reported.
According to the police, the initial investigation revealed that the fire erupted due to the vehicle's malfunctioning air conditioning system.
The passenger bus was on its way from the port city of Karachi to the Khairpur Nathan Shah area of the Dadu district of the province when it encountered the fatal incident.
Police, rescue teams and firefighters rushed to the site, put off the fire, and shifted bodies and injured to the Liaquat University Hospital in Jamshoro.
The police official added that nine women and eight children are among the deceased persons.
The hospital officials feared that the death toll might rise because several of the injured were burnt severely and were in critical condition.
There were 55 passengers on board who belonged to the same village located in the Khairpur Nathan Shah area.