Police said that the building of the blanket manufacturing factory, located in the city's Focal Point area, collapsed following a blast in the factory's boiler around midnight Sunday.
Over 70 workers were inside the factory -- Sheetal Fibres -- when the building collapsed.
Over 45 workers had been rescued till Monday morning. Many of them had injuries and thus admitted to hospitals here for treatment, said Deputy Commissioner Priyank Bharti.
Initial rescue efforts were hampered by the location of the factory being in a congested area and due to darkness.
A worker, with serious injuries, was rescued from the debris, officials said.
Rescue teams of the district administration were trying to rescue the remaining trapped workers. The rescue work was being carried out by personnel of the fire brigade and police.
The district administration has sought the help from the National Disaster Response Force (NDRF) and the Army for rescue and relief operations. However, the NDRF team was yet to reach the collapse site Monday morning (at 7 a.m.)
The deputy commissioner said that the exact number of trapped workers was being ascertained. He said that the exact cause of the collapse was yet to be found.
"Information from the factory owners revealed that there were 60-70 workers inside the factory when the building collapsed," Bharti said.
Rescue and relief operations were continuing despite early morning rain in the city.