Terror struck Lahore for the third time in two months when an explosives-laden vehicle apparently targeting the ISI headquarters went off in crowded Civil Lines area, killing at least 30 people and leaving nearly 150 injured. 

Police officials said 10 people have been killed but the privately run rescue organisation Edhi Foundation put the death toll at 35.

The pick up truck could not reach the ISI building and blew off at a barrier close to the complex.

Reports said some suspects picked up in connection with the March 3 terror attack on the visiting Sri Lankan cricket team here, were inside the ISI office when the blast took place.

Security forces have cordoned off the area and shifted the injured and bodies to hospitals. Emergency has been announced in local hospitals.

"It was a suicide car bomb attack," Lahore city police official Omar Ahmad said.

The injured lay trapped and helpless underneath the debris after the attack in the city's commercial district.

The chief of Lahore city administration, Sajjad Bhutta, said the attacker tried to breach a road block and get close to the building.

"A vehicle bomb exploded just outside the police rescue offices, destroying the office, damaging nearby buildings and injuring people," he told reporters.

Local television showed images of frantic crowds gathering around devastated buildings, some reduced to piles of rubble, while other structures had their windows blown out by the force of the blast.