"It's a tragedy," Bernard Sévigny said, adding the city lowered its flag to half-mast out of respect for those injured and killed.
"Today, the first thoughts go to the families, the workers."
The cause of the blast is under investigation.
Sévigny said there are still containers of acetone at the plant, which has been largely reduced to a pile of debris.
"Our firefighters are on the site today to try to get the containers out of the plant," he said.
"There is a lot of work to do and [that could take] the whole weekend."
Massive fire followed explosion
The blast happened at about 1:30 p.m. ET at Neptune Technologies et Bioressources Inc., located in an industrial area on Pépin Street.
The company makes health products from krill oil, which contains omega-3 fatty acids.
The explosion sparked a massive fire that took emergency crews hours to get under control and triggered fears of toxic exposure due to the acetone at the site.
Environment Quebec later said the fumes from the fire were not toxic and local residents should not be worried.
2 killed, 17 injured
When rescue workers entered the building, they found the bodies of two people, as well as a woman in severe shock.
In total, 17 people were rushed to Sherbrooke University Hospital Centre with injuries ranging from shock to severe burns.
The hospital's director of nursing said Friday morning that the majority of those patients had since been released from hospital. Two remained at the facility to be treated for shock.
Four others were transported to Montreal for treatment of burns.
Sévigny said the plant employs more than 100 people, and the impact of the human loss and the damage to the building is being felt throughout the community.
The mayor said he met with the company's directors earlier Friday and their staff is struggling to fully understand what has happened.
"It's quite difficult for everybody here," he said.
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