According to reports the fire broke out at 5 am GMT (10.30 am IST) and completely engulfed the the ground floor, including parts of the first floor of the building in Tabernacle Street.
However, no casualities have been reported in the fire as the building was empty when the incident too place.
Though the confirmation on the cause of fire is being awaited, it has been assumed that the fire was caused by an electrical short circuit.
London Fire Brigade said that over 100 firefighters along with about 20 fire engines are making efforts to control the fire.
The Metropolitan Police have cordoned off the various roads area, along with part of City Road south of Old Street, Bloomberg Square and Worship Street.