A woman is in critical condition after her arm was severed in industrial blast at a gravel pit in Shawnigan Lake on Vancouver Island.

An explosion at Mid Island Aggregate on Tuesday afternoon sent rocks flying 400 to 500 metres toward a group of people who were then injured, said RCMP Sgt. Rob Webb.

The woman in her 50s had her right arm severed near the elbow, said Webb.

Two men in their 40s and early 50s were also taken to the Victoria General Hospital where they are in stable condition.

"I can say the one male that was hit in the head, likely the hard hat saved his life," said Webb.

Blasting is common at the Shawnigan Lake gravel pit but witnesses said the explosion was unlike ones they had heard before. CBC

Blasting is common at the gravel pit but witnesses said the explosion was unlike ones they had heard before.

"Today's blast was unusual. It was loud and shook our whole building," Charlie McGill, manager of Westland Industrial. "We got up from our desks, ran outside and that's when we noticed the rocks coming down onto our lot."

Rocks bigger than baseballs rained down onto businesses in the industrial area below the gravel pit.

"It felt like a car bomb went off or an earthquake," said Lisa Channell, who works at an aggregate company nearby. "They blast up there all the time and we don't usually feel anything from it. So something went horribly wrong."

"It definitely reverberated into the chest," said Bill Shifflett, who was working at a neighbouring mill. "It wasn't a scheduled blast because there was no typical beep beep beep seven times and then seconds, maybe thirty seconds, and then boom! That's when the blast hits."

The Ministry of Energy and Mines and WorkSafeBC are investigating.