Local residents were told to stay indoors and to keep windows and doors shut after the massive cloud engulfed the Belgian suburb.
A sharp smell of burned waffle caused coughing in the city centre, about four miles away, after the blaze broke out in a Milcamps plant in the Forest municipality this afternoon.
So far nobody has been injured in the blaze, but the damage is extensive. The 50 staff present at the factory at the time were evacuated and are all safe.
Photos from the city showed the dense, black cloud lying low over the horizon and smothering the landscape, disrupting rail traffic across Brussels.
One person told Twitter they were left stuck at the Eurostar station because of the smoke, saying: “And our journey home! Stuck the Eurostar at Brussels station, delayed because of the smoke from this waffle conflagration!”
Another tweeted: “The smoke had spread pretty far before I left that spot. I’m not sure how it looks now. Hopefully it’s under control!”
Around 200 students from a local school and employees from nearby companies have also been evacuated, along with those living in houses near the factory.
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The huge smoke cloud broke out over Brussels after a fire
“The fire has caused a thick plume of smoke that is potentially toxic,” Forest Mayor Marc-Jean Ghyssels said.
Firefighters raced to the scene to battle the blaze but they were unable to save the burning factory.
Pierre Meys, spokesman, said: “The building is completely lost. There are no victims, the factory had been evacuated before the fire brigade arrived.”
Police said the blaze at the Milcamps factory, which produces the national sweet treat in various regional variants, broke out at lunchtime. It was not immediately clear what started it or whether anyone was hurt.
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Photos from Brussels showed the dense, black cloud lying low over the horizon
A police official said: “A significant amount of smoke is visible and we have asked [the local] population to close doors and windows and to stay inside.”
The fire at the Milcamps factory is believed to have originated in the cooling system and quickly spread.
An investigation into the blaze will now be launched.
It is feared the huge smoke cloud could be carrying toxic chemicals.
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The fire at the Milcamps factory is believed to have originated in the cooling system
But as of 3pm, it is reported there have not yet been an increase in concentrated pollution in Forest.
Environment Minister Céline Fremault said: “The weather conditions today are particularly favorable to the dispersion of pollutants”
Train traffic was completely stopped for nearly 40 minutes at the exit of Brussels-Midi, towards Nivelles, Mons, Charleroi, Halle or even Ghent.
But railway services have now resumed shortly before rush hour, although trains must cut their ventilation.
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Local residents were told to stay indoors and to keep windows and doors shut
Drivers have also been urged to turn off their ventilation as it’s unclear how dangerous the smoke is.
Belgian waffles, traditionally sold from mobile vendors and street kiosks, have become popular around the world.
They are batter cooked between hotplates patterned according to various regional traditions and dusted with icing sugar.
Their history dates back to the wafers baked for Mass in the medieval monasteries of the Low Countries.