There has been no casualty, said fire services minister Sovan Chatterjee, who is also the city mayor. Eight people were taken to a local hospital, six of them were released after First Aid. Two, who fell sick from inhalation of smoke, have been admitted.
The fire broke out at the third-floor of the building -- called Aspirations -- in the offices of the Gas Authority of India Limited around 1 pm, sources said.
Ten fire tenders were pressed into service to control the blaze - an operation that took more than an hour. The fire tenders had trouble making their way through the narrow lane.
Asked about the troubles faced by the fire tenders, Mr Chatterjee said, "Kolkata has just six or seven per cent road space. Despite that, what the fire brigade managed to do is to make the impossible possible."
The cause of the fire is not yet known.
Asked if the building's fire alarms not work, the Mayor said, "Many allegations come at a time like this. There was a big jewellery store, many big offices... We will investigate the matter".
A nearby school, Abhinav Bharati High School, has declared a holiday tomorrow.