The explosion took place as Hazaras, who are Shiite Muslims, were buying vegetables early on Friday morning, Quetta police chief Abdul Razzaq Cheema told Al Jazeera.
"Members of the Hazara community go to the market every day to shop, and we provide them with a security escort," he said.
"They were at the market as police and (paramilitary) Frontier Corps soldiers patrolled the area. There was a store selling potatoes, and that is where the explosion has taken place."
Images from the scene of the explosion showed blood sprayed across the dirt floor of the market, damaged vehicles and sacks of potatoes split open by the force of the blast.
Cheema said police would not know whether the bomb was planted or a suicide attack until investigating teams, who had cordoned off the site, completed their analysis.
At least seven members of the Hazara community and one paramilitary soldier were among those killed, he said.
Since 2013, more than 509 Shia Muslims - mainly ethnic Hazaras - have been killed in a campaign of targeted shootings and bombings in Balochistan province, according to government data.
The majority of attacks have occurred in the provincial capital, Quetta, where most of the country's roughly 600,000 Hazaras reside.
The city's Hazara residents now live in two heavily protected enclaves on either side of the city, with movement outside of those areas restricted by threats to their lives.
In October 2017, unidentified gunmen opened fire on a van bound for the fruit and vegetable market, killing the driver and four others, police say.
No group immediately claimed responsibility for the attack on Friday.