Interior Minister Balochistan Sarfraz Bugti told ARY News that it was a huge blast but he can not say anything about the nature of blast.
At least 14 people - including seven policemen - lost their lives, while 19 others were injured in a suicide blast that shook Shuhada Chowk in Quetta's Gulistan Road area in June.
The huge intensity of the explosion smashed windscreens of many vehicles parked near the blast site.
All the injured were shifted to Civil Hospital Quetta for treatment and rescue operations are underway.
While 12 people were reported to have died on the spot, dozens were left wounded. The nature of the blast could not immediately be determined but an investigation was underway, he said.
It cited army chief General Qamar Javed Bajwa as saying terrorists were trying to disrupt Monday's celebrations of 70 years of independence from Britain.
"Incendiary explosive was used in the blast due to which nearby vehicles caught fire", ISPR reported.
There was no immediate claim of responsibility for the attack, however Taliban militants, and Baloch separatists have been involved in attacks on security forces in the recent past.
Minister Bugti said firefighters were still working to put out the blaze.
Sanaullah Zehri, Chief Minister (CM) of Balochistan, who accompanied ousted premier Nawaz Sharif at Data Darbar rally in Lahore at the time of the untoward incident said that all hospitals in the area were operating in state of emergency to counter the tensed situation.
The province has also seen a number of attacks carried out by the Lashkar-e-Jhangvi's Al Alami faction, a group with ties to ISIL, known for attacking Shia Muslims.