Four small bombs have exploded near a popular theatre in the Pakistani city of Lahore, all detonating within 15 minutes of each other, police say.

At least six people were reported to have been injured by the blasts that blew out the windows of the buildings around Al-Falah theatre hall on Friday.

The area was immediately sealed off by the police. Ambulances were seen rushing to the scene as people raced away from the sound of the blasts.

Police said the bombs appeared to be crudely-made and that the theatre was closed at the time of the explosions.

"Luckily there was no serious damage," Pervaiz Rathore, the police chief of Pakistan's second-largest city, said.

Kamal Hyder, Al Jazeera's correspondent in Pakistan, said the explosives were planted in a nearby drainage channel .

"The explosions were meant to send a message rather than wreak havoc," our correspondent reported.

"[But] there is a big question mark remaining as to who could have planted the bombs."