The fire which had reportedly been 'cleared' by the capital's fire department on Sunday re-emerged before it was finally contained by the efforts of firefighters and the Pakistan Navy.

Two people were killed and at least five injured after the fire erupted initially in the morning.

The building, located close to the PTV headquarters and a five-star hotel, houses several private and government offices and was declared the Software Technology Park 1 earlier.

Initial reports stated that the fire erupted in the upper floors of the six-storey building, however, later officials said the fire began on the ground floor near an office of the Federal Tax Ombudsman.

The record placed in the ombudsman's office was also said to have been completely destroyed.

Rescue officials said the two people who died did not need to jump from the building as a fire exit was available. They added that the two worked at a call centre inside the building and were injured from the fall.

They were shifted to separate hospitals but succumbed to their injuries.

Seven fire tenders were on site to douse the flames the first time around, according to rescue officials.

The firefighters were able to extinguish the blaze in around an hour and later continued the 'cooling efforts' after which they left the venue. However, when rescue teams began going floor-by-floor, sparks led to another fire which was fanned by ongoing winds in the city.

Acting Islamabad Deputy Commissioner Farasat Ali Khan, said that when the cooling operation was under way on the third and fourth floors, the fire restarted after it received oxygen as the doors were opened by rescue staff.

The fire was reportedly caused by short-circuiting but investigations will determine the exact cause of the flames.