A gas explosion at a building housing an ice cream factory and apartments in eastern Pakistan early Tuesday killed at least 25 people and wounded 20, police and rescue officials said. Rescue workers were sifting through the rubble for at least three others feared trapped inside.

The three-story building in Lahore (search), that also housed workers' quarters and low-end apartments, collapsed in the blast.

City police chief Aftab Cheema said it was not immediately clear what triggered the explosion. Survivors, some in critical condition, said that gas cylinders had been stored in the building's basement.

Cheema said eight of the 25 people killed were from the same family, who were sleeping in an apartment on the building's second story.

Three or four nearby homes and several vehicles were damaged.

Mohammed Afzal, the official in charge of the rescue operation, said the blast happened at about 3 a.m. and was heard around Lahore, the capital of Pakistan's eastern Punjab (search) province.

"We have been told that dozens of people were inside the building at the time of the blast. We are trying to save as many people as possible," he said.

He expected it would take another four hours to clear the debris.

"We are using cranes and bulldozers. We are very careful because some people are still believed buried in the rubble," he said, as grieving relatives and residents wailed and cried for their loved ones.

Zubair Chattha (search), a senior police official, told The Associated Press that the rescue teams had pulled out 25 bodies from the rubble after a 15-hour operation. "They have seen three more bodies in the basement where the blast occurred. Despite darkness, they are trying to reach the spot to look for the survivors," he said.

The building housed a small ice cream factory whose 12-15 workers usually slept on the front lawn but had stayed inside last night because of heavy rain.

"First I heard a big explosion, and then saw the roof falling. I don't know what happened next, but when I opened my eyes, I was on a hospital bed," said one of the workers, Munib Ahmad, 25, recovering at Lahore's Jinnah Hospital. His head was bandaged.

Other survivors at the hospital said the building owner had ignored repeated requests to move the gas cylinders that were stored in the basement.

"We always feared that it would happen one day," said Sardar Ahmed, 34, who was sleeping on the second floor when the blast occurred. "He never paid any attention to our requests."

The owner, a retired academic, could not be reached for comment.

City mayor Mian Amir Mahmood (search) told reporters that he had ordered an investigation and that those found responsible would be punished.