POLK COUNTY, Fla. -- A combination of thick morning fog and brush fire smoke on Interstate 4 in Polk County apparently sparked a 70-car pileup that killed four people and injured at least 38 others.

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PHOTOS: Sky 6 Images | Crash Scene
TRAFFIC: Alternate Routes

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"We have a major disaster that has occurred on Interstate 4," Polk County Sheriff Grady Judd said. "Our firefighters and EMTs went into an environment where you could not see absolutely anything in front of you. It was as if you were hitting a wall of smoke and fog. As a result of that, there have been at least 50 vehicles involved in the major event. You could not see your hand infront of your face and that is not an exaggeration."

Authorities said brush fires created smoke that combined with fog, sparking a series of crashes near Old Grade Road in Polk County before rush hour Wednesday morning.

Officers on the scene said they could not reach people trapped in their cars as they burned.

"(The officer) said, 'I did all I could do but I watched a man burn to death today and I heard others screaming and crying,'" Judd said. "And (the officer) said, 'I can't begin to explain to you how difficult this scene was and I can't begin to explain to you the trauma that occurred and I did all I could'"

Officials said there were at least 82 people injured in the pileup and there could be more than 3 deaths involved in the crashes.

"Florida Highway Patrol said billowing smoke from brush fires and thick fog in the area may have reduced visibility to zero," Local 6's Tiffany Tift said. "Included in this pileup are cars, trucks and more than 12 tractor-trailers and a total of 10 vehicles are on fire. Again, 50 vehicles involved and several vehicles on fire as well."

Local 6 showed video of a tractor-trailer on fire and burning near County Road 557.

"At least one person was trapped under one of the damaged tractor-trailers," Tift said.

"This is a brush fire that actually came onto I-4 and we have multiple reports of vehicles and tractor-trailers that are on fire," Local 6's Kim Sanders said.

Fire rescue workers said they were having a hard time getting to the crash scene because of thick fog and smoke.

"It's been very difficult to see out there," county representative Cindy Rodriguez said.

Florida Highway Patrol officers said visibility in the area was down to zero at the time of the crash.

More than 100 emergency units were called to the crash scene to assist the injured.

Nearly 15 miles of I-4 between Tampa and Orlando were blocked, authorities in Lakeland said.

The interstate was closed in both directions near Polk City.

Drivers were urged to avoid the area Wednesday morning.

Watch Local 6 News for more on this story.