Firefighters remain on the scene of a factory fire in midtown Toronto after a massive blaze engulfed the industrial building on Thursday, causing an estimated $6 million in damage.

The fire broke out shortly before 8:30 a.m. at Foamco Industries, a mattress factory on Fairbank Avenue, near Dufferin Street and Eglinton Avenue West.

Fire officials have been unable to examine the rubble left from the massive blaze because crews have been working to control the fire for almost 24 hours.

The fire, which is believed to have started near the office, quickly ripped through the large building, but it is believed that company's 50 employees were unharmed.

Approximately 430 firefighters and over 130 fire trucks were on scene as the six-alarm fire burned out of control.

Firefighters entered the building when they arrived, but parts of the roof and walls started to cave in, so they had to fight the flames from outside the burning building.

As a wall of thick black smoke poured from the factory, nearby residents were asked to stay indoors. Eight schools were placed under a "shelter in place" order, meaning children were kept inside for recess, windows were shut, and ventilation systems sealed.

There have been no reported injuries related to the blaze.

There were concerns that the smoke may be toxic, as the burning gel, memory foam, and natural latex mattresses burned.

When the location is deemed safe, the Ontario Fire Marshal will investigate the cause and origin of the fire.