Pakistani President Asif Ali Zardari's security chief was killed in a suspected suicide bomb attack in the volatile port city of Karachi as he stopped his armoured vehicle to buy some fruit, police said.

A senior officer said Bilal Shaikh was killed with two other people in a prosperous area of eastern Karachi. About a dozen others were wounded.

"It seems the suicide attacker walked up to Bilal Shaikh's vehicle and blew himself up outside the front passenger seat of the vehicle where Mr Shaikh was seated," said police officer Raja Umar Khattab.

Pakistan has been hit by a spate of bombings since Prime Minister Nawaz Sharif was sworn in last month, underscoring the challenges facing the nuclear-armed nation in taming a Taliban-linked insurgency.

A police escort was accompanying Mr Shaikh's white armoured sports utility vehicle when the attack took place. No one immediately claimed responsibility.

Mr Shaikh, who had survived an earlier assassination attempt near his home in Karachi a year ago, used to change his routes several times while travelling around Karachi.

Both Mr Zardari and Mr Sharif have condemned the incident.