The blast targeted a truck carrying the officers on the outskirts of Quetta, the capital of Balochistan, provincial home minister Mir Sarfraz Bugti told reporters.
He said it was premature to say if it was a blast triggered by remote control or a suicide bombing.
Local media, however, quoting unnamed police officials, reported the blast could be the act of a suicide bomber.
Footage aired on local Geo TV showed charred wreckage of the truck lying in the middle of the road, while honking ambulances shifted the dead and injured to hospital.
Waseem Baig, a spokesman for the Civil Hospital Quetta told reporters that at least 10 injured -- several critically -- were admitted.
One hour after the bomb blast, another police officer was killed in an ambush by unknown gunmen in a busy locality of Quetta.
A Tehrik-e-Taliban Pakistan (TTP) statement later claimed responsibility for the Quetta blast, claiming one of its suicide bombers targeted the police in retaliation for alleged extra-judicial killings of its members in custody.
The large Balochistan province, which is also considered to cover parts of neighboring Iran and Afghanistan, is strategically important because of the rich presence of copper, zinc and natural gas.
It has been beset by violence for over six decades, with separatists claiming it was forcibly incorporated into Pakistan upon the end of the British rule in 1947.
2 soldiers killed
Various sectarian outfits, including Lashkar-e-Jhangvi, have also been active in the region, especially in Quetta, for the last decade.
Also on Wednesday, at least two soldiers were killed in an improvised explosive device (IED) blast in northwestern Waziristan tribal agency near the Afghan border.
"Army convoy was on its way when an IED bomb went off near the army vehicle in Khajori area of North Waziristan," a local political administration official told Anadolu Agency over the phone on condition of anonymity due to restrictions on talking to media.
The military did not confirm or deny the incident.
In a statement, a faction of the outlawed Pakistani Taliban -- Tehrik-e-Taliban Pakistan Sheharyar group -- claimed responsibility for the blast.
This is the second such attack on security forces in the last one week in North Waziristan.
At least three soldiers had been killed and seven others wounded on Oct. 9, when a military convoy came under attack in Dosli area of North Waziristan.
North Waziristan, one of the seven semi-autonomous tribal regions in Pakistan has been a battleground between the army and the Taliban since June 2014 following the launch of a full-scale military offensive.
Pakistan army had declared the area clear from militants since September 2016, and said all militants had been wiped out from the area -- which once was a stronghold of Pakistani and foreign militants.
According to Pakistan army, almost 3,000 militants have been killed in the operation in North Waziristan that left more than 200 troops dead from 2014 to 2016.