Pakistani police say a roadside bomb targeting a senior judge has killed at least four people and wounded seven others in southern Pakistan.

Senior police official Ameer Sheikh says the Sindh High Court judge, Maqbool Baqir, was wounded in Wednesday's attack in Karachi, the capital of southern Sindh province.

He says Baqir was going to court when a bomb attached to a motorcycle went off near his vehicle.

The dead included one of the judge's guards. Police officers and passers-by were among the injured and dead.

TV footage showed authorities transporting victims of the attack to hospitals.

The bomb also damaged nearby shops.

No one claimed responsibility for the attack.