Two people have died after an explosion and fire at a plant in Sherbrooke, Que. Another 19 people were injured, five with severe burns.

The explosion, which occurred at a Neptune Technologies & Bioressources facility, caused the fire.

The two dead were found in the rubble hours after the blast.

Two of the burned were airlifted and two others rushed by ambulance to a specialized unit at a Montreal hospital.

The cause of the explosion is unknown, but several smaller explosions followed the initial one, which was so violent it was heard across the city and set a local record for 911 calls, according to Gaetan Drouin, a local fire chief.

Martin Carrier, a Sherbrooke police spokesman, said more than 100 people in Sherbrooke and surrounding suburbs phoned within a minute.

"Just looking at the damage to the building you can see it was probably very violent," Drouin said.

"I was working in my garage and I heard a loud, 'Boom.' Then we were evacuated," a local resident said.

Another resident said the flames could be seen from blocks away. Neither resident wished to be identified.

The fire left the facility in a smouldering pile of rubble, with the remaining walls scorched black.

The fire struck the plant's 15,000 litres of acetone reserves, causing concern about toxicity because the substance is flammable and can cause irritation if ingested.

Although thick black smoke could be seen coming from the plant for kilometres, tests revealed the smoke did not contain toxic chemicals.

It took 50 firefighters hours to contain the flames and access the facility.

Neptune Technologies & Bioressources produces and exports health products derived from marine life like Omega-3.

"We're in terrible shock over what's happened," Michel Chartrand, chief of operations for the company, told reporters at a press conference Thursday evening.

He added that plant officials will work with authorities to determine what caused the incident.

“We want to understand what happened,” he said.

With files from The Canadian Press