A government official says death toll from a collapsed factory building in the eastern Pakistani city of Lahore has risen to 37 after rescuers found more bodies in the rubble.

The official, Mohammad Usman, says so far rescuers have saved 103 people.

He says rescue crews were carefully cutting steel and picking through concrete on Saturday to reach several workers believed to be still trapped.

Usman's comment came a day after a teenager, whose family assumed he was dead, was found after 50 hours trapped under the rubble of the four-story factory which collapsed on Wednesday. The cause of collapse is yet to be determined.

The building caved in just over a week after a magnitude-7.5 earthquake hit Pakistan, killing 273 people and damaging nearly 75,000 homes.