What was already expected to be one nightmare of an afternoon commute just got so much worse with the closure of a major Toronto highway.

Ontario Provincial Police say that at least 20 cars were involved in a series of collisions along Highway 401 near Kelso Conservation Area this afternoon, resulting in the complete closure of all the busy road's westbound lanes.

At least 15 passenger vehicles and seven transport trucks were involved in the pileup, according to OPP Sgt. Kerry Schmidt. Miraculously, no one was seriously injured.

Pile up - #Hwy401 WB blocked west of #Hwy25 due to multi vehicle collision. 20 vehicles involved including transpor… https://t.co/MU6jAILFmu

— Sgt Kerry Schmidt (@OPP_HSD) February 13, 2019

Schmidt described "whiteout conditions, blowing snow [and] big fluffy flakes" in announcing the crash around 1 p.m., implying that weather may have played a factor.

"All lanes are blocked, there is no access," he said of the 401 in a live Periscope video from the scene. "If you're travelling westbound, you want to get off before you hit Highway 25.

"We've got about 10 km of backed up traffic," he continued. "This is going to be a major delay, major cleanup."

Stuck in the westbound highway 401 mess Milton to Kelso pic.twitter.com/WtTOQul2I3

— John McClean (@Northof9) February 13, 2019

Police announced that the lanes had reopened around 3:15 p.m. this afternoon, though it's still a good idea to avoid the 401 near Milton if you can.

Westbound Traffic is once again moving, but firefighters, paramedics, investigators and tow trucks remain on site cleaning up the mess.

Halton Regional Police are helping OPP officers investigate the incident and control the overflow traffic into Milton.

"We are assisting with traffic once it gets off the highway," said Halton Police Const. Ryan Anderson to CBC Toronto shortly before the highway reopened.

"The drivers are flooding the roads of Milton."