Firefighters were trying to douse the flames when the the factory collapsed, trapping 15-20 people, police officials said.
"Four bodies have been pulled out," Deputy Commissioner, Ludhiana, Pradeep Aggarwal said.
The victims have been identified as Inderpal Singh, Fire Officer Simaon Gill and firemen Rajan and Puran Singh, he said.
Rescue operations are underway and could continue throughout the night.
Earlier in the morning, at least 15 fire tenders were rushed to the spot to control the fire.
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Senior district administration and police officials are present at the site.
Punjab Chief Minister Amarinder Singh said he was "shocked and saddened" by the factory collapse incident.
"Shocked and saddened at the Ludhiana factory collapse. Have asked district administration to extend all help to NDRF in rescue operations," he tweeted.
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