At least 16 people were killed and 30 wounded on Friday by a powerful blast apparently targeting the Shia Hazara ethnic minority at a crowded fruit market in Pakistan's Quetta city, officials said.

Body parts littered the scene and injured people screamed for help as black smoke cloaked the market after the explosion.

No group has claimed responsibility for the attack, but Balochistan - which borders Afghanistan and Iran - is Pakistan's largest and poorest province, rife with ethnic, sectarian and separatist insurgencies.

Provincial police chief Mohsin Butt said eight Hazara were among the 16 victims.

The Hazara, whose Central Asian features make them easily recognisable, are a soft target for Sunni militants, who consider them heretics.

They are so frequently targeted that they are forced to live in two protected enclaves in the city and are given a daily police escort to the market to stock up on supplies.

Police chief Butt said the same had happened on Friday.

The bomb detonated near a site where produce was being loaded for distribution around the market.

'A huge bang'

"I was loading a small truck and I heard a huge bang and it seemed as if the earth beneath me had shaken and I fell down," said Irfan Khan, a labourer, from his hospital bed.

"The atmosphere was filled with black smoke and I could not see anything, I could hear people screaming for help and I was also screaming for help."

He said the air was "filled with the stinging smell of burnt human flesh".

Senior police official Abdul Razaq Cheema said the blast targetted the Hazarganji neighbourhood of Quetta.

Hazara make up roughly 500 000 of the city's 2.3 million people.

Amnesty International said the blast was a "painful reminder" of the many attacks suffered by the Hazara community in Quetta over the years, and called for the government of Prime Minister Imran Khan to give them better protection.

"Each time, there are promises that more will be done to protect them, and each time those promises have failed to materialise," wrote Omar Waraich, Amnesty's deputy director for South Asia.

Violence in Pakistan has dropped significantly since the country's deadliest-ever militant attack, an assault on a school in the northwestern city of Peshawar in 2014 that killed more than 150 people, most of them children.