Twenty people were killed and six others injured in a devastating fire on the first two floors of a building housing a market, a godown and offices in Sealdah area in the metropolis in the early hours on Wednesday.

West Bengal disaster management minister Javed Ahmed Khan told reporters here that 20 persons were killed in the blaze and six injured, with the condition of two critical.

The fire was detected at 3:50am in the 25-year-old Surya Sen Market complex when some shopkeepers and labourers working in the market were fast asleep, with the blaze spreading from ground floor to the floor above, vice-chairman of the market Sushanta Ghose said.

The staircase of the market was blocked with goods making it difficult for people trapped inside to escape, Ghose said.

He said there was only one proper entry and exit and though there was one emergency exit, it was not used for the last 15 years.

Local people said they were alerted by shouts of people trapped inside the building.

"When I came out of my house after hearing screams, I saw flames leaping out and people shouting from the windows," Ranjit Hazra, a resident of the area, said.

According to fire department officials, plastics, paper and cloth were stored in the godowns in the building.

The ground floor and the first floor which sustained the maximum damage housed 200 shops.

The fire services minister, who rushed to the spot and supervised fire-fighting operations, said firemen and police cordoned off the building and the blaze was brought under control in three hours by 26 fire-tenders.