A suicide attack in southwestern Pakistan has killed at least four people and injured 10 others, officials say.

Thursday's blast occurred when a motorcyclist rammed his explosives-laden vehicle into a police Armoured Personnel Carrier (APC) carrying deputy police chief, Rao Anwar, in Karachi.

Anwar survived the attack near a bank in the south Asian nation's financial capital.

"The attack was against me. I was moving with my squad in Malir Halt district when the explosion took place. I am unhurt, but some of my men have been injured," Anwar told the AFP news agency.

He claimed to have been threatened for a month by "unknown terrorists".

"It was a suicide attack," police official Tahir Naveed told the AFP. "The attacker was killed in the blast and the body in hospital is suspected to be his," he added.

The Pakistani Taliban, Tehrik-e-Taliban (TTP), have claimed responsibility for the attack.

Karachi, home to 18 million people, is Pakistan's largest city.

Karachi's port was heavily utilised by US forces fighting the Afghan Taliban across the border, until Islamabad shut down the supply lines last November following a US air strikes that led to the deaths of 24 Pakistani soldiers.

The last bomb attack in the city killed three soldiers in December.