A chemical reaction at an industrial fertilizer factory near Sheppard Avenue West and Highway 400 caused an "unknown vapour cloud" to be released into the atmosphere this morning, according to Toronto Fire, leaving orange-coloured smoke coursing through the air. 

Emergency crews responded to the factory on Gail Grove around 10:50 a.m. Wednesday morning, and Highway 400 between Highway 401 and Finch Avenue was shut down in both directions shortly after. 

Level 3 Haz May call at this industrial fertilizer factory.A chemical reaction occurred that resulted in the release of an unknown vapour cloud into the atmosphere. A number of buildings have been evacuated as a precaution and Toronto Police and the OPP have shut down a number ro pic.twitter.com/RKESnAjjAU

— Toronto Fire Service (@Toronto_Fire) April 14, 2021

Toronto Police also closed all surrounding roads, including Sheppard from Weston Road to Jane Street in both directions and all side streets leading to Sheppard Avenue, Laura Road, Torbarrie Road, Arrow Road and Rivalada Road.

Highway closure #Hwy400 between Finch and #Hwy401 https://t.co/JeFL1E9IYk

— OPP Highway Safety Division (@OPP_HSD) April 14, 2021

"@toronto_fire is advising to avoid the area due to potentially highly toxic fumes," wrote police in an update around 11:40 a.m. "@TTC has been updated and redirecting service."

Something is happening at 400 and Sheppard area. Not good! @CP24 @CTVNews @globalnewsto pic.twitter.com/MX7EUdnRax

— Jennifer Di Francesco 🇨🇦🇮🇹 (@jendifrancesco) April 14, 2021

A number of buildings in the area were also evacuated. 

About an hour later, Toronto Fire asked residents in the area to shelter in place while they investigated further. 

Fortunately, a spokesperson for Toronto Fire told the CBC that the cloud would safely dissipate on its own, and Highway 400 reopened around 12:35 p.m.

FIRE: (UPDATE)
400 N + Sheppard Ave W
- Arrow Rd has re-opened#GO683911
^ep2

— Toronto Police Operations (@TPSOperations) April 14, 2021

All affected roadways have since reopened to vehicles, and no injuries have been reported.