Agrawal, who supervised the rescue operation, said substandard construction material used could be the reason for the chimney collapse.

The Balco management and GDCL officials avoided visiting the crash site throughout Thursday fearing attacks by workers.

At the site, dozens of workers and women were beating their chests and crying, fearing the worst for their kin and colleagues.

'It came crashing like thunder. For a moment, I thought it was the sound of thunder as it was raining heavily at the time. But I soon realised that it was the chimney that was coming down,' Dayaram, a 28-year-old worker, told IANS at the Balco hospital where he was recovering from his injuries.

He was near the crash site when the tragedy struck around 4 p.m. Wednesday. Both his legs were fractured as he was hit by parts of the chimney.

'I was in a group of eight colleagues. We began running to avoid the crumbling structure. I can't believe I am alive,' said the contract worker from Bihar's Vaishali district.

Korba district police chief Ratanlal Dangi said the chimney had reached the height of over 100 metres before it caved in amid lightning and heavy rain.

Balco has annual production capacity of up to 345,000 tonnes aluminium. Once a public sector firm, now Sterlite Industries (India) Ltd holds 51 percent stake in Balco, while the remaining stake is held by the Indian government.