Faridabad Deputy Commissioner Balraj Singh said the number of casualties and those injured could rise further as more workers were feared trapped in the debris.
The rescue operation was on, he added.
The injured have been admitted to various hospitals in Faridabad, where the condition of one of them was serious.
Those killed included Gopal (25) and Deepak (35), both from Bihar.
Police Commissioner S Kapur along with the Deputy Commissioner supervised the rescue operation. Haryana Labour Minister Shivcharan Sharma also visited the scene.
Sources said the 500 sq yd plot on which the school was coming up was originally a playground, but the SRS management allegedly leased it out to Sukhversa Malhotra of Delhi, who was constructing the school.
Faridabad SDM S Sarwan said a criminal case would be registered against the SRS management and Sukhversa Malhotra.
A team from the National Disaster Relief Force (NDRF) was requisitioned in the evening to speed up the rescue operation.
Around 300 police personnel, including jawans from the HAP, were engaged in the rescue operation. Over five fire tenders and JCB machines were also pressed into service.
The Residency Towers comprises over 10 multi-storeyed buildings. As a precautionary measure, the authorities have temporarily evacuated the two towers adjoining the ill-fated school building.
Gopal Mishra, a vegetable vendor who witnessed incident, said the structure crashed suddenly, leaving little time for the workers
to escape.
The authorities said the exact cause of the collapse was not yet known but suspected inadequacy of plinth or sandy nature of the soil to be behind the accident.
Ground Zero
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SRS Residency Towers in Sector 88 comprises over 10 multi-storeyed buildings
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Finishing touches were being given to the building when it collapsed
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The 500 sq yd plot where the school was coming up was originally a playground, but was leased out to Sukhversa Malhotra of Delhi
