The 18-storey Infinity Benchmark building in Sector V had a brush with disaster on Wednesday when a fire broke out barely two hours before the offices there would have been bustling with 3,000-odd workers ranging from techies to telemarketers.

The first trails of smoke were detected on the sixth floor at 6.40am, when only one office located on the top floor had opened for the day.

Sources said the Sector V fire brigade station, located 200 metres away, sent seven engines and a skylift within 20 minutes of being alerted by a guard who had spent the night in the building. Evacuation of those inside was prompt but the fire raged for two more hours, by which time many employees had gathered below to gape at the smoke-filled building and contemplate what might have been.

Nobody was injured in the blaze and only a portion of an office was gutted, official sources said.

The first two floors of the building has retail outlets, pharmacies and ATMs while floors three to five are reserved for parking. Between the sixth and top floors, there are 32 offices.

An official of Infinity Infotech Parks, which constructed the building and remains in charge of its maintenance, confirmed that some employees of an office that was open through the night had to be rescued by the fire brigade.

"An office on the top floor, ICRA Online, was open at the time of the fire and about 10 of its employees and some security personnel of other companies weren't able to come down because of the smoke. They were evacuated through one of the three staircases," he said.

Many workers who had heard about the fire arrived late, knowing that they wouldn't be let in. Scores of others stood away from the building and spoke about how the timing of the incident saved them. "I shudder to think what would have happened had the fire broken out during the day because my office is on the 14th floor," said an employee of Suraksha Diagnostic Pvt Ltd.

"Our office opens at 9.30am but I was running late this morning. When I arrived, my first thought was that this was a film shoot," recounted an employee of Amrit Feeds, in whose office the fire is suspected to have started because of a server short-circuit.

Uday Saha, 27, had been asleep in a room adjacent to Amrit Feeds' office on the sixth floor when he woke up feeling suffocated. "I rushed out and the corridor was filled with black smoke. I covered my nose and mouth and somehow found my way down the staircase," he said.

G.P. Ghosh, director of fire services, said the "fire preparedness" of the building was satisfactory. "Smoke detectors, hydrants, hoses and sprinklers were working. There is also an underground reservoir."