A late-night fire that spread from a decorator’s warehouse to an adjoining fast food factory killed at least three workers, with more than 20 feared trapped inside, on Calcutta’s southeastern fringes off EM Bypass.

While the flames had been extinguished before noon on Monday, firefighters had till late evening been unable to enter either building, each stifling hot and filled with smoke from a heap of smouldering debris.

The three charred bodies pulled out — probably they did not lie deep inside the gutted buildings in Nazirabad Road near Anandapur — remain to be identified.

Baruipur police said in the evening that 21 other workers, reported missing by their families and friends, were feared to be inside.

It was not clear whether the 24 caught in the fire were working or sleeping inside.

The fire department received the first call around 2.30am on Monday. A dozen fire tenders that fought the blaze found the fast food factory locked and had to break its door.

Anxious families of the workers gathered outside.

The initial rescue efforts began only in the afternoon after the flames had been extinguished, but failed to make much headway in the heat and smoke generated by the smoulder.

The fire is believed to have started from the warehouse, belonging to a decorator named Pushpanjani, and spread to the other building, stashed with food and soft drinks.

Fire officials said they had spotted cooking utensils and stoves inside the warehouse that could be the source of the fire. The exact cause can be ascertained only by forensic experts, fire officials said.

People in the neighbourhood said they had heard several gas cylinders explode.

Anxious and angry families of the missing — Krishnendu Dhara (from Pingla), Raju Manna (Tamluk), Sujit Singh (East Midnapore) and Basudev Haldar (Baruipur) — demanded the immediate removal of the debris to speed up the rescue.

“We want the debris removed. Else, how shall we know whether our loved ones are trapped inside?” said a relative of Anup Pradhan, 32, a Pingla native employed at the decorator’s warehouse.

Sujit’s family said they had last spoken to him at 11pm on Sunday. Since then, his phone has been switched off.

Basudev, a father of three, last spoke to his family on Saturday. He was to return home on Monday.

Police sources said it would take a few days to clear the entire area of the debris.

“The fire is under control now, but the smoke has to be let out. KMC officials are removing the debris,”power minister Aroop Biswas said.

A senior officer at the Baruipur police directorate said: “Three bodies have been taken out; the rescue effort is inprogress.”