At least three people died in traffic accidents in the area of a 70-car pileup in Wisconsin on Sunday.

Authorities are still unsure what caused the backup in Germantown, where at least 70 cars and trucks driving in snowy and icy conditions slid out of control or were held up, the Los Angeles Times reported.

The Wisconsin Department of Transportation caught the deadly incident with a video that shows traffic inexplicably backing up and then cars continuing to speed down the highway until they crash.

At one point in the clip, a car slides completely off the highway and into brush on the side to avoid hitting any other vehicles, the L.A. Times reported.

The area saw several major traffic accidents on Sunday, and at least three people died altogether due to collisions. At least one man died from injuries suffered in the 70-car pileup.

Officials are warning people not to take action during such incidents, but to stay in their cars instead. During Sunday's 70-car pileup, motorists were leaving their vehicles to look at the accidents, talk to other motorists or to take pictures.

People involved in traffic incidents need to "either to find a way to drive out of the area slowly and safely and report the accident to law enforcement or to remain inside the disabled vehicle until help arrives," authorities said.

The competing emergencies stemming from the high number of traffic incidents kept law enforcement agencies "pressed to the limit."

More than 100 vehicles were involved in crashes in Germantown on Sunday, according to the Milwaukee-Wisconsin Journal Sentinel.

"We are still getting calls today," Chief Peter Hoell told the Journal Sentinel on Tuesday. "If their vehicle was drivable, we try to get them off the highway right away. Others just left."

The cause of the fatal pileup may never be known, he said.

"Some people don't even know which vehicle they hit, they were crashing and spinning out," Hoell said. "We may never know who caused it and if we don't know, then it would be difficult to issue a citation and prove that in court."

As winter approaches, motorists should be cautious while driving in snowy conditions and stay in their cars when involved in traffic collisions.

Also on Sunday, a massive car pileup in Pennsylvania left one motorist dead. After a two-vehicle crash, one of the drivers got out to check on the people in the other car when a passing vehicle hit the victim, who was pronounced dead at the scene, authorities said.

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