At least two people have been killed and 27 injured in an explosion at the main railway station in the eastern Pakistani city of Lahore.

Rescue sources said that 35 people were taken to hospital after the bomb blast. Five of the wounded were in criticial condition, said officials.

Television footage showed a waiting room littered with glass and upended furniture. The windows had been blown in by the force of the explosion.

The bomb went off outside the business class ticket counter at platform 2.

It is not clear who planted the bomb, but police believe it was an act of terrorism.

Lahore chief of police Aslam Tareen said that the bomb contained 6-8kg of explosives and had yielded a high-intensity blast. "We will investigate how this occurred," he said. "With the security checks in place, this should not have happened."

"The bomb was planted in a bag which was left near one of the counters at the station," Tareen told Reuters. "We're trying to investigate how the bag managed to get through despite so many scanners."

President Pervez Musharraf released the statement condemming the attack: "I strongly condemn the blast at the Lahore railway station and offer my sincerest condolences to the families of the innocent lives lost. The government should take strict measures to curb such violent acts."

Islamist militants have carried out bombings across Pakistan in retaliation for military operations targeting insurgent groups in recent years.

In January 2011, at least 11 were killed in a suicide bomb attack on a Shia procession in Lahore.