Interstate 70
Police vehicles fill an off ramp along Interstate Highway 70 as they try to prevent demonstrators from entering the highway near Ferguson, Missouri, Sept. 10, 2014. Scott Olson/Getty Images

Multiple people were killed Thursday in a crash involving 12 cars and three semi-trailers on I-70 near Denver West Parkway, Colorado.

According to Lakewood Police Department spokesman Ty Countryman, the crash was reported around 4:50 p.m. local time (6:50 p.m. EDT), after an eastbound speeding semi-trailer collided with slow moving traffic on the highway. After one of the vehicles involved in the crash burst into flames, the fire began to spread.

"We have to try and figure out why this happened," Countryman said. "The semi coming into the slower traffic. There's got to be a reason. We'll investigate and find out."

The police have not confirmed the exact number of fatalities, but they have stated that there were more than one. Six people, including the driver of one of the semi-trailers were transferred to a local hospital. There were no updates regarding their condition.

A YouTuber, who goes by the name Burger Planet, was live streaming when he captured the moment a white semi-trailer sped past his vehicle, toward the crash site. After a few seconds, the video cut to an enormous plume of black smoke rising from where the crash happened.

Aerial videos of the scene showed multiple semi-trucks and at least two SUVs on fire beneath a bridge and piles of lumber scattered along the highway.

Countryman confirmed that there was significant damage to the structure of the bridge. “The bridge was not impacted from the collision; it’s all from the heat of the fire,” he said

The highway was closed overnight as authorities worked to clear debris from the area.

Although the fire had been put out, investigators were prevented from getting close to the crash due to the hot spots that were still being actively monitored by firefighters. "We still are just getting to the wreckage," Countryman said.

One witness told NBC News no one was sure of what was going on immediately after the crash. "I was trying to get to the off ramp, and just all you hear is this big huge boom and then the big black smoke just kind of went off all over," the witness said. "And then you start hearing this popping noise, and things blowing up. It was just really scary. Nobody really knew what was going on."

I-70 is a major east-west highway that passes through states like Colorado, Kansas, Missouri, Indiana, Ohio, Pennsylvania and Maryland.

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