The deceased include four women. Seven others were rescued by fire service personnel.
Hyderabad District Collector Amoy Kumar said the victims died of suffocation due to the smoke.
The deceased, all stated to be in their 20s, succumbed at Gandhi Hospital. They hailed from Warangal, Mahabubabad, and Khammam districts and were said to be employees of a company operating out of the building.
After battling for four hours, fire fighting personnel controlled the fire which started from the third floor of Swapnalok Complex and spread to the upper floors of the eight-storey building, which houses offices.
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Officials said the rescue work was still on as the smoke has not yet cleared.
Ten fire tenders rushed to the scene and were engaged in the fire-fighting operation.
Huge flames leaping out of the building, causing panic among people in the area. Police vacated residents staying in adjoining buildings.
According to locals, the fire broke out between 7.30 and 8 p.m. The cause of the fire was not known.
State minister T. Srinivas Yadav rushed to the spot and was monitoring rescue and relief work.
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This is the second major fire accident in Secunderabad, the twin city of Hyderabad, in less than two months.
Three persons were killed in a huge fire at a multi-storey commercial complex on January 28. The building was completely gutted in the fire and it was later demolished by the authorities as the structure had become weak.(IANS)