Several others are feared trapped. The injured have been shifted to a nearby hospital while rescue operations have been taken up on a war-footing.
Police said the under construction building at Kasavanahalli suddenly collapsed about 3.30 pm, trapping many. Fire brigade and police personnel, who were informed, launched rescue operations assisted by local people.
Bengaluru Mayor R Sampath Raj said two labourers were found dead under the debris while one of the rescued succumbed to injuries in hospital.
Deputy commissioner of police of Whitefield division, Abdul Ahad said the building belonged to one Rafique from HSR Layout.
"We are gathering more information.It was developed to accommodate paying guests but later the owner tried to convert it into a commercial building," he said.
The deputy commissioner said that the construction had started six years ago but was stopped midway and six months ago, the construction began.
It is learnt that there were labourers from other states as well. It is said that the building collapsed because of weak foundation.
"Rescue team is at work.... the rescuers have gone inside the building," he said.
"We will initiate action against the owner and the contractor but our priority is to rescue people trapped under the debris," Raj said.