LAHORE, Pakistan — A bomb planted by suspected Islamic militants exploded at a filling station in Pakistan's central Punjab province Tuesday, killing at least 20 people and wounding 127 others, police said.

Many of those hurt remained trapped by debris and shrapnel hours after the blast reduced the station building to rubble, with rescue workers hurriedly trying to heave stones and metal away to rescue survivors.

"We fear the death toll may rise because the condition of some of the injured is very critical," said Aftab Cheema, regional police chief in Faisalabad, the country's textile-making capital.

"It was a car bomb blast. The explosive was planted in a car," Cheema said.

Eyewitness Ijaz Hussain told reporters at the site that he heard and felt a loud blast before chaos ensued.

"It was a deafening blast -- I thought the ground had been jolted by an earthquake. Everybody was running here and there to save his life. I saw injured people and dead bodies scattered here and there," said Hussain.

Television pictures showed the station had been reduced to a pile of bricks and gnarled metal as rescue officials worked to remove rubble from the scene to search for survivors and ambulance vehicles ferried the injured away.

An administration official at the scene, Liaqat Chatta, told AFP by telephone that the entire station building collapsed and many vehicles there were completely destroyed.

"Five other buildings close to the station were also badly damaged and part of the buildings collapsed. The rescue operation is still continuing and we are searching for people trapped in the rubble," he said.

City commissioner Tahir Husain told private Geo television that rescue officials were heaving bricks and metal away with cranes and other machinery.

Husain told private TV channel Waqt that no suicide attacker was involved.

"It was not a suicide attack. It was a planted bomb blast. The bomb exploded near the gas cylinders that triggered a bigger blast," he said.

Husain said that the attack may have been aimed at government buildings close to the filling station, which sold compressed natural gas for vehicles, adding that some of the buildings were damaged in the blast.

Pakistan has been wracked by violence in recent years, mostly targeting security officials.

Some 4,000 people have been killed in bomb blasts, suicide and gun attacks blamed on Taliban and Al-Qaeda fighters since Pakistan troops stormed a militant mosque in Islamabad in July 2007.

On Saturday at least one person was killed and another wounded when a bomb exploded in a house in Pakistan's biggest city of Karachi.

Faisalabad city is near the home of a Christian government minister who was buried Friday after being killed in a hail of bullets in Islamabad last week over his opposition to the country's strict Islamic blasphemy laws.

His assassination sparked international outrage and stoked concern about rampant militancy and rising extremism throughout the nuclear-armed nation, a fractious ally in the US-led war in Afghanistan.