“Massive fireball, massive explosions and a chain reaction.”

Struggling to describe what happened Tuesday night on Highway 400, OPP Sgt. Kerry Schmidt called the fiery crash that killed at least three people “the most unbelievable scene” he had ever witnessed.

It all started on the highway north of Highway 88, at around 11:30 p.m. Several northbound lanes were closed because of a rollover three-vehicle collision, involving an impaired driver.

“[Officers] observed a massive collision, followed by a fireball just behind them in the ensuing traffic,” Schmidt said.

A total of 14 vehicles were involved in the pileup, including at least two fuel tankers

“At least one of the fuel tanker trucks slammed into the back of slow moving or stopped traffic just behind this collision scene causing the fireball, causing the explosions,” he said.

Schmidt said the fiery crash was so intense it twisted metal. Almost nothing is left of some vehicles.

“The vehicles are completely destroyed; melted into the asphalt. There is nothing left of these vehicles, short of twisted metal and steel.”

Schmidt says fuel leaked from the tankers and fire flowed down the highway.

“People were literally running for their lives to not be encompassed by the moving fire that was on the highway and was down in the ditch.”

The flames were finally extinguished at around 2 a.m. after burning for nearly two and a half hours.

“The temperatures achieved in this fire were apocalyptic. It is unbelievable to see that kind of damage and destruction from a motor vehicle collision.”

With three confirmed dead, officers are still scouring the scene for other potential victims.

The exact cause of the crash is still under investigation, but Schmidt says their initial probe points to inattentive driving as a possible leading factor.

Highway 400 is going to be closed between Highway 88 and 89 for several hours, while emergency crews examine the scene and crews rebuild the damaged highway.

Emergency detours have been set up in the area.

Officials say the northbound lanes of the highway might not be open until Thursday morning.

Thousands of litres of fuel also leaked into the soil and ground water around the highway.

Witnesses recount what they saw

Nicholas Marrs and his girlfriend were driving on the highway from Toronto when they got caught in the aftermath of the crash.

“It was horrible. We saw a giant flash of orange light. When we looked up we saw this transport truck, the whole highway just engulfed in flames,” said Marrs.

He said flames spread to the forest and were moving towards them.

The crash happened just 500 metres in front of Sara Hlywka.

“The sky went yellow,” she says. “If I didn’t break as hard as I did and if I didn’t veer off then I would have been dead.”

She believes if she was going any faster, she would have been caught in the crash. She believes someone was watching over her.

“I think it changed my perspective of life and I think I’m going to hug my children a little tighter because if it wasn’t for them I don’t think I would have stopped the way I did.”

She phoned her family to tell them she was OK, but they thought the worst.

“They thought I was calling to tell them this was my time to go, but it was me telling them I was safe.”

"I've worked here 25 years and I don't remember ever being at a collision as wide scale as this one with the type of damaged that we witnessed," says County of Simcoe Paramedic Services Commander Kevin Morrish.

He was one of the first at the scene. The horrific crash is etched into his mind.

"It is a bit hard to grasp because after a certain amount of time you start to internalize what you saw and you start to think of your family and your friends and what you do if you're in that position  and I think that takes a bit of a toll on people."

A coroner’s inquest request

During a news conference on Wednesday morning, Premier Kathleen Wynne passed on her condolences to the victims.

“It was a horrible tragedy. My heart goes out to all the victims and their families,” she said.

She says her government will be advised if there’s more that can be done to prevent these deadly crashes.

Progressive Conservative Leader Patrick Brown shared his condolences on Twitter and called for a coroner’s inquest.

With files from CTV Toronto and The Canadian Press.