Watch: Feds probe Fort Worth 133-car pile-up which killed six in Texas

Federal authorities in the US are investigating the causes of a 133-vehicle pile-up in the Texas city of Fort Worth that killed six people.

Dozens more were hurt in the crash on Interstate 35 last week, which took place during a snowstorm.

The National Transportation Safety Board said their investigation is focused on the snow and ice treatment procedures.

At least five people were killed when up to 100 vehicles were caught in a pile-up during a wintry storm in Fort Worth, Texas.

Before the crash the road had been treated with brine, essentially salty water, used to dry roads before cold weather.

North Tarrant Express, the private company managing the road, said it was following the same procedure as the Texas Department of Transportation.

“NTE & NTE35W maintenance crews started pre-treating the corridors on Tuesday morning in anticipation of inclement weather, and have been treating continuously as they monitor the roadway,” the company said in a statement.

“We will continue treating the highways through the weekend and into next week, as long as the storm is active.”

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.

“There were multiple people that were trapped within the confines of their vehicles and requiring the use of hydraulic rescue equipment to successfully extricate them,” Fort Worth Fire Chief Jim Davis said.

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

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

Mr Zavadsky said his crews carry a sand and salt mixture in the ambulances, which they used at the scene. At one point, he said, one of the ambulances was hit, but it sustained only minor damage and the crew members were fine.

Numerous others were treated at the scene and released, he added.

The crash happened about 6am local time, 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.

Texas, including Fort Worth, has been shivering through a highly unusual bout of freezing cold weather.

Much of the massive state is now without power, with gas and coal plants malfunctioning from the freezing temperatures. 9news