DALLAS - A massive crash involving more than 130 vehicles on an icy Texas interstate left six people dead and dozens injured Thursday amid a winter storm that dropped freezing rain, sleet and snow on parts of the U.S.

At the scene of the crash on Interstate 35 near downtown Fort Worth, a tangle of semitrailers, cars and trucks had smashed into each other and had turned every which way, with some vehicles on top of others.

At least 65 people were treated at hospitals, with 36 of them taken by ambulance from the crash site, including three with critical injuries, said Matt Zavadsky, spokesman for MedStar, the ambulance service for the area.

The crash happened about 6 a.m., as many hospital and emergency workers were heading to and from work, so some of those involved were health care workers and emergency responders, including police officers, officials said.

“We did see a large number of people that were victims of this accident that were in scrubs, that had hospital IDs on … in some cases, our folks would know those folks,” Zavadsky said.

Fort Worth police Chief Neil Noakes said three officers were en route to work when they were injured in the crash, and one officer was injured while working the scene. He said all have been released from the hospital and that none of them suffered serious injuries.

“The roadway was so treacherous from the ice that several of the first responders were falling on the scene,” Zavadsky said.

The ice storm came as a polar vortex moved near the U.S.-Canada border, resulting in colder weather farther south than usual, said Steve Goss, a meteorologist with the National Weather Service’s Storm Prediction Center.