The fire at the SynAgri warehouse started at around 2:30 a.m. Wednesday.The fire at the SynAgri warehouse started at around 2:30 a.m. Wednesday. (CBC)

Toxic smoke from a fire at a fertilizer and herbicide plant in Lévis, south of Quebec City, has forced about 50 people from their homes.

The blaze broke out at the SynAgri warehouse in the city's Charny district at around 2:30 a.m. Wednesday and quickly spread out of control, completely destroying the facility.

"People who see smoke around their homes due to the fire, we're asking them to stay inside," said Lévis fire department spokesman Yves Despés.

He said residents should turn off air conditioners and keep the windows closed.

The nearby Le Etchemins High School was also shut down for the day as a precaution.

Despés said no further evacuations would be required.

Despite the efforts of 60 firefighters, the warehouse is a complete loss, said SynAgri president Jean-Claude Brulotte.

"At this time of the year our inventory is pretty low because it is the end of our season," he said.

No injuries were reported.

The cause of the fire is unknown.