At least 19 people were killed and 11 others injured when a speeding passenger bus veered off a mountain road in heavy rain and fell into a ravine in Pakistan's restive Balochistan province on Sunday.

The bus carrying more than 30 people was heading to Quetta from Islamabad when it plunged into the ravine in Zhob.

Television footage showed rescue workers assisting bloodied passengers.

As the bus neared Quetta, the driver lost control at a sharp bend and the bus plunged into a ravine. We have recovered 19 bodies so far while 11 injured have been admitted to hospital, Assistant Commissioner Syed Mehtab Shah said.

Rainfall and speeding led to the incident, The Express Tribune newspaper quoted Shah as saying.

Rescue teams rushed to the scene soon after receiving information, Shah said, adding that the bodies had been taken to the hospital where the process to identify them was underway.

The medical superintendent of Civil Hospital Zhob, Dr Noorul Haq, said that the injured were in critical condition and the death toll could rise.

Balochistan Chief Minister Mir Abdul Qudoos Bizenjo expressed grief over the accident. He ordered an emergency be declared in Civil Hospital Zhob to ensure treatment for the injured.

Prime Minister Shehbaz Sharif also expressed sorrow over the tragic accident and offered his condolences and sympathies to the bereaved families of the deceased.

The premier directed the authorities concerned to provide immediate medical aid to the injured.

Deadly accidents are common in Pakistan owing to poor road infrastructure, disregard for traffic laws and poorly maintained vehicles.

Last month, 22 people were killed, including nine members of a family, when a passenger van fell into a ravine near Qila Saifullah district of northern Balochistan.