Karachi: At least 12 people were killed and 28 others feared trapped under the debris and rubble of a four-storey building that collapsed in the congested Lyari area of Pakistan's port city of Karachi.

Police and rescue officials said they were working overtime and still trying to remove the debris and rescue people trapped underneath the four-story building collapsed on Thursday.

City commissioner Mohammad Hussain said rescuers had dug out 12 bodies so far from the building rubbles but there were still around 28 people trapped underneath the collapsed structure.

"We are doing our best to ensure we can take them out alive but lack of space and the contested area are making rescue efforts very difficult," he said.

The building in Moosa lane collapsed due to decay and illegal structures constructed on the premises.

At the time of the collapse, there were 78 people in the building but rescuers said majority had been rescued on time due to help from the Army Engineering Corps which came in with heavy duty machinery to clear the debris and rubbles.