According to reports, a roadside bomb exploded just as a police vehicle carrying 35 police personnel was passing from Sariab Mill area on the Quetta-Sibbi Road.
A forensic team from Lahore is expected to reach Quetta soon to determine the nature of the blast, he said.
Talking to media, Balochistan Home Minister Mir Sarfraz Bugti said that such terrorist attack could not shake the resolve of eliminating the militants.
The injured officers were being treated and some of them were in a critical condition, said doctor Mohamed Farooq at the Quetta Civil Hospital.
Security forces reached the site and cordoned off the area after the explosion.
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He added, "Terrorists plan their activities from Afghanistan while India's Research and Analysis Wing (RAW) along with Afghanistan's National Directorate of Security (NDS) facilitate the terrorists carrying out their attacks in Pakistan".
Later in the day, unidentified gunmen shot dead CTD Police Inspector Abdul Salam at Qambrani Road of the provincial capital, said police.
"The people and government of Balochistan will not be deterred from the fight against terrorism", Zehri said, adding the fight will continue till the last terrorist remains. On August 13 this year, at least 15 people, including eight soldiers, were martyred when a military truck was targeted in Quetta.
Prime Minister Shahid Khaqan Abbasi also strongly condemned the terrorist attack in Quetta and directed authorities to provide best possible medical treatment to the injured.
Earlier in June, 14 people - including seven policemen - lost their lives in a suicide blast that shook Shuhada Chowk in Quetta's Gulistan Road area.
Pakistani leaders, including Imran Khan, and members of the civil society condemned the attack, praying for the victims.