The attackers targeted the convoy of security forces on the Sariab road in the provincial capital Quetta, they said.
The police confirmed that it was a suicide bomb attack on security forces convoy, the Geo News reported, adding five people were killed in the incident.
"The target was the vehicle of the Frontier Corps commander, but he was not present in the vehicle when the bomb attack took place," a government official said.
The fifth person is believed to have died later at the hospital.
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"Some of the injured are still in critical condition as they were hit by shrapnels in the attack," Baig said.
The attack came a day after senior police official of Khyber-Pakhtunkhwa Ashraf Noor was killed in a suicide attack on his vehicle in the upscale Hayatabad neighbourhood of Peshawar.
No group has claimed responsibility for the attack but Taliban militants and Baloch nationalists often target security forces in the area.
Senior Superintendent of Police (SSP) Muhammad Illyas who was on his way to market when he was killed in a targeted attack along with his wife, son and five-year-old granddaughter.
A suspected suicide bomber killed Additional Inspector General Telecommunications Hamid Shakeel and three other police officers in a targeted attack in Quetta on November 9.
Balochistan has been rocked by a series of attacks which raised concerns about a growing militant presence, including those affiliated with Islamic State, which has claimed several bombings in the restive province.
At least six police commandos and a civilian were killed last month when an explosives-laden vehicle rammed into a security force's convoy on the Quetta-Sibi Highway.
In August this year, a massive suicide explosion, targeting Pakistan Army personnel in Quetta, left 15 people dead including seven civilians and injured at least 20 people.
In June this year, 14 people, including seven policemen, were killed and 21 others were injured in a suicide car bombing on Gulistan Road in Balochistan.