The explosion took place inside Gulbahar police station in Peshawar. – AP (File Photo)

PESHAWAR: A seemingly accidental blast that Pakistani police blamed on “toilet gases” damaged a police station in the city of Peshawar on Monday, injuring at least five people.

A police official initially said the blast occurred in a room used to store ammunition in the station in the neighbourhood of Gulbahar in the main city in Pakistan's Taliban-infested northwest.

But the Peshawar police chief later told incredulous reporters on television that dodgy sewers were responsible for the collapse of one room and the partial damage of two others.

Television footage showed civilians and policemen carrying injured people out on stretchers and ambulances rushing to the scene.

Northwestern Pakistan is frequently hit by bomb attacks blamed on Islamist militants opposed to the government's alliance with the United States that have killed more than 4,200 people across the country since July 2007.

But Peshawar city police chief Liaqat Ali blamed Monday's blast on “gases in the toilets”.

Asked if gases could be strong enough to demolish two rooms of a police station, he insisted: “It happens in many cases.”

Local administration official Muhammad Siraj Khan told AFP that a natural gas leak in the sewars within the police station caused the blast.

“The blast triggered a fire in a nearby room which had electricity controls,” he said.

“Five people, including four policemen and one prisoner, were injured,” he added.