At least six people are dead and three dozen injured, some critically, following a devastating 130-plus car pileup on Interstate 35 West in Fort Worth on Thursday morning. Freezing rain and drizzle are probably to blame, with slick roadways posing a serious danger to travel.

The Fort Worth Fire Department described the accident as a mass casualty incident, meaning local first responders were overwhelmed by the response needed to treat the number of those injured.

All northbound lanes of the highway were closed to traffic as crews responded to the accident, with reports of multiple people trapped and concerns of hypothermia if victims were not removed from the vehicles quickly. The accident occurred around 6 a.m.

Police expressed concern that a number of passengers still trapped in their cars shortly before 11 a.m. were at risk for hypothermia. Authorities were beginning the lengthy process of “entangling” the heap of vehicles and locating additional victims.

The Fort Worth Police Department confirmed more than 130 vehicles, including more than a dozen semi-tractor-trailers, were involved in the crash.

At a midmorning news conference, police and fire personnel repeatedly asked for prayers for the families of victims. By the afternoon, 65 people were being treated at nearby hospitals for injuries related to the crash, said MedStar spokesman Matt Zavadsky.

Police opened a reunification meeting point at the Riverside Community Center in Fort Worth.

Ambulances accessed accident victims from the north and south, transporting them to different hospitals depending on the direction from which they approached. Fourteen ambulances and an ambubus were utilized.

Horrific video posted to social media showed mangled vehicles piled atop one another, with some left as unrecognizable heaps of twisted metal. Some vehicles were facing one another head-on, indicating probable spinouts in the slick conditions leading up to the crash.

Bud Kennedy, a longtime reporter at the Star Telegram, described the episode as a “calamity,” tweeting, “It is the single worst chain-reaction car and truck crash I have seen here, like something out of a disaster movie. My prayers to all involved.”

Behind the accident, traffic was backed up for more than eight miles, and authorities diverted vehicles off the highway. It was one of numerous accidents and closures reported across the Dallas-Fort Worth metroplex Thursday morning.

Temperatures at the time of the crash were in the low to mid-20s with high relative humidity — a textbook setup for freezing drizzle.

A weather balloon launched from the National Weather Service forecast office in Fort Worth reveals temperatures as high as the mid-50s in a layer of air just 4,000 feet above the ground. That has allowed rain to fall as liquid, freezing on contact with the surface in the shallow, frigid layer near the ground.

Complicating matters even further is that Dallas-Fort Worth is known for its raised highways and overpasses. Elevated roadways are the first to freeze during freezing-rain events, because cold air can chill them from above and below. Moreover, they don’t have the benefit of any remnant surface heat from the otherwise warmer ground preceding the storm.

That makes it easy for conditions to vary over short distances from safe and ice-free to slick and dangerous.

The National Weather Service had issued a winter weather advisory, writing that “people are urged to remain at home and avoid travel unless necessary.”

On Wednesday night, the agency called for up to a tenth of an inch of ice accretion.

“Very slippery sidewalks, roads, and bridges are possible,” read the advisory. “Hazardous conditions are ongoing and will persist into the afternoon.”

Paulina Villegas contributed to this report.