At least four people were injured in a blast outside a mosque on Quetta's Sariab Road on Friday, police said.
The wounded were shifted to the Civil Hospital for treatment. The incident took place after Friday prayers.
A video showed worshippers coming out of the mosque as an explosion was heard and plumes of smoke rose from a motorcycle on fire.
Quetta Deputy Inspector General Abdul Razzaq Cheema said the nature of the explosion could not be immediately ascertained and police were investigating if explosives were planted on a bike or if the vehicle caught fire.
But another police official told DawnNewsTV that 1-1.5 kilogrammes of explosive material was left in a bag next to a motorcycle parked outside the mosque. He said the blast was caused after the detonator blew up but the explosives themselves didn't catch fire.
More destruction would have been caused if the explosive material had gone off, the official added.
Police cordoned off the area as the probe into the blast went underway.
According to state-run APP news agency, shops were shut down as panic gripped the area following the blast. Rescue services were also dispatched to the site.