A suicide car bomber killed at least seven people, including four police officers, in an attack near a checkpoint in the volatile southwestern Pakistani city of Quetta on Friday, officials said.

Abdul Razzaq Cheema, director general of police in Baluchistan province, told Reuters it appeared the bomber had detonated a car packed with explosives. He said 15 people had been wounded.

"Seven dead bodies have been brought to the Civil Hospital in Quetta and at least five people are in critical condition," Cheema said.

Four of those killed were police officers, while nine security officials were among the wounded, said Fareed Sumalan, a doctor at the Civil Hospital.

Baluchistan government spokesman Anwar ul Haq Kakar said the blast happened near the office of the inspector general of police when officers stopped the car to search it near a checkpoint.

"It's possible the IG office was the target, or the assailants were trying to enter the (army) cantonment which is close by," he said.

Television footage showed emergency services rushing to the scene, which was covered in debris, while security officials cordoned off the area.

Quetta is about 100 km (60 miles) east of the border with Afghanistan and is the capital of Baluchistan, which has been plagued by militant violence. The province is the base of a separatist movement as well as home to the Taliban and other militant Islamist groups.

It is also at the centre of Chinese-backed "Belt and Road" development projects worth $57 billion that first focussed on Chinese firms building roads and power stations but is now expanding to include setting up industries.

Militants from the Islamic State group abducted and killed two Chinese nationals in Quetta last month.

That attack prompted Pakistan to boost security around Chinese nationals and other foreigners in the province, which is already one of the most militarised regions in the country.