Story highlights The toll from the fire has risen to 289, a local official says

The building could collapse at any time, another official says

Dozens of people may still be trapped in the factory's basement

Fire officials say they don't yet know the cause of the fire

At least 289 people were killed in a fire that swept through a garment factory overnight in the Pakistani port city of Karachi, a local official said Wednesday.

The toll from the fire, which continued to burn Wednesday, is expected to rise, Commissioner Roshan Ali Shaikh, Karachi's top administrative official, said in a phone interview with CNN affiliate Geo TV.

A child is among the dead, and at least 25 people have been injured, said Zakir Khan of the Karachi Fire Department. All the victims were employees of the factory, he said.

Firefighters were trying to bring the blaze under control, Khan said, but their task was made more difficult because they couldn't enter several portions of the weakened building.

The building might collapse any time because the fire heavily damaged parts of its steel structure, said Mustafa Jamal, a senior government official in Baldia Town, the area of Karachi where the factory is situated.

Photos: Karachi factory blaze kills 289 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – Aziz Ahmed, the father of factory worker Asif Aziz who was killed in a blaze in Karachi Wednesday, September 12, 2012, holds his son's photo as he mourns his death. Hide Caption 1 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – Pakistani Muslims offer funeral prayers of at least 289 garment factory workers who were killed after fire engulfed the building in Karachi. Hide Caption 2 of 12 Photos: Karachi factory blaze kills 289 Deadly fire in Pakistan – An undamaged area of a garment factory following the fire. All the victims were employees of the factory, said Zakir Khan of the Karachi Fire Department. Hide Caption 3 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – Pakistani rescuers remove the body of a garment factory worker. One child is among the dead and at least 25 people have been injured, Khan said. Hide Caption 4 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – Pakistani firefighters extinguish a fire that erupted in a garment factory. At one stage, firefighters feared dozens of people were trapped in the building's basement. Hide Caption 5 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – A Pakistani woman mourns the death of her relatives in the fire. Between 400 and 500 people were in the factory as it burned. Several trapped workers jumped from upper floors, said Mustafa Jamal, a senior government official in Baldia Town. Hide Caption 6 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – A Pakistani man mourns the death of relatives. Video broadcast by Geo TV showed large crowds of anxious people outside the smoldering building. Hide Caption 7 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – Emergency crews work at the scene of a deadly fire at a garment factory in Karachi, Pakistan, on September 12. Hide Caption 8 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – Pakistani residents watch the rescue operation in the garment factory in Karachi. Officials say they don't know the cause of the fire. Hide Caption 9 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – Emergency crews work at the scene of a deadly fire at a garment factory in Karachi, Pakistan, on September 12. Hide Caption 10 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – A Pakistani woman mourns the death of relatives in the fire. Hide Caption 11 of 12 Photos: Karachi factory blaze kills 289 Fire engulfs Karachi factory – Emergency crews work at the scene of a deadly fire at a garment factory in Karachi, Pakistan, on September 12. Hide Caption 12 of 12

Dozens of people may be trapped in the basement of the building, according to Khan. An operation is under way to try to rescue them.

Jamal said between 400 and 500 people were in the factory as the fire burned. Several trapped workers jumped from upper floors.

Video broadcast by Geo TV showed large crowds of anxious people outside the smoldering building. And through windows and holes of the factory's scorched outer walls, the footage showed glimpses of flames still flickering within.

Officials say they don't know the cause of the fire.