Police and the provincial government said a tanker exploded outside the Karachi Airport - which is Pakistan's biggest - on Sunday.

The provincial home minister, Zia UI Hassan, told local television station Geo News that it was an attack targeting foreign nationals.

Pakistani separatist militant group the Baloch Liberation Army (BLA) claimed responsibility for the explosion, according to the Reuters news agency.

The group said it was targeting Chinese nationals and was carried out using a vehicle-borne improvised explosive device.

Footage of the blast showed flames engulfing cars and a thick column of smoke rising from the scene.

Rahat Hussain, who works in the civil aviation department, said the explosion was so big it shook the buildings of the airport.

Karachi police deputy inspector general East Azfar Mahesar told reporters that it seemed like it was an oil tanker explosion and said officers were among the injured.

"We are determining the nature and reasons for the blast. It takes time," he said.

The BLA seeks independence for the province of Balochistan, located in the southwest of Pakistan, bordering Afghanistan and Iran.

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In August, the group launched coordinated attacks in the province, in which more than 70 people were killed.

The BLA specifically targets Chinese interests, as thousands of workers are in Pakistan, many involved in Beijing's multibillion-dollar Belt and Road Initiative that connects south and central Asia with the Chinese capital.

In the past, the group has accused Beijing of helping Islamabad exploit the Balochistan province.

The attack came a week before Pakistan is set to host a summit of the Shanghai Cooperation Organisation, a security grouping founded by China and Russia to counter Western alliances.