Pakistani police say a powerful bomb has exploded near security forces guarding a famous Sufi shrine in the eastern city of Lahore, killing at least four people and wounding several others.

City police chief Ghazanfar Ali says police officers were the apparent target of Wednesday's bombing outside the shrine which is known as Data Darbar. He says hundreds of pilgrims were inside and outside the shrine when the blast took place.

TV footage showed a badly damaged police vehicle that authorities said was the target.

Lahore is the capital of eastern Punjab province.