Exclusive video has emerged of a toxic scare involving workers at a construction site in Port Adelaide, with tradies heard coughing and spluttering while shrouded in a cloud of cement dust.

The dramatic footage shows a sudden blast erupting at the worksite on Friday, with a thick cloud of cement powder swallowing the area within seconds.

A worker can be heard calling out “where are you?” as he’s engulfed by the dust, coughing and barely able to see through the toxic cloud.

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WATCH THE VIDEO ABOVE: Workers shrouded in cloud of cement dust.

The CFMEU says the worker was shrouded in highly toxic silica dust and may have even been exposed to carbon monoxide.

“There are no safe levels of exposure of silica,” CFMEU’s Travis Hera-Singh told 7NEWS.

“It appears that people weren’t wearing or weren’t provided adequate PPE.

“If I was exposed to that, I’d be concerned about the level of exposure,” Adelaide University’s Dr Lloyd Dadd said.

Workers shrouded in cloud of cement dust. Credit: 7NEWS

The union says a pipeline fault triggered Friday’s incident, putting dozens of workers at risk.

“Potential 44 people exposed in this one incident,” Hera-Singh said.

“Workers were offered the opportunity to go home, but it would have been without pay.”

Hallard Group has told 7NEWS it followed all proper safety protocols, saying the work area was immediately evacuated and SafeWorkSA was called in to investigate.

In a statement, the company said the “incident presents a low health risk, with the cement containing less than 0.5 per cent respirable silica”.

SafeWorkSA has placed restrictions on the site until it’s deemed safe.