A North Charleston mother and her twin teenage daughters were trapped Monday afternoon when a cement truck landed on top of their car and cement poured inside, hardening while rescue workers tried to dig them out.

"I've never seen anything like this before," said Peter Rogers, public information officer for the Charleston County Volunteer Rescue Squad.

Authorities said the accident on Interstate 26 killed the mother and one of the 15-year-old sisters, who was driving the car. Charleston County Coroner Rae Wooten identified them as Christina Akabidavis, 42, and Marcushire Akabidavis, 15.

The mother was in the front passenger seat, said Cpl. Paul Brouthers of the S.C. Highway Patrol. He said the 15-year-old twin, who was in the back seat, was taken by helicopter to Medical University Hospital in critical condition. Authorities did not release her name, but a previous story in The Post and Courier identified her as Maurishire Akabidavis. The same story said the twins attended Porter-Gaud. They turned 15 on Saturday, according to their online Facebook profiles.

Drivers can get their beginner's permit when they turn 15.

The driver of the cement truck, Jeffrey Mobley, 39, of Bowman, was in good condition Monday night at Trident Medical Center, the hospital said.

"He was shook up," Brouthers said.

The crash happened at about 3:10 p.m. in the eastbound lanes in front of the rest area near College Park Road. The family's red Honda made an abrupt lane change in front of the cement truck, Brouthers said. He said the truck driver tried to compensate, but struck the Honda and the truck landed on its side on top of the car.

The teenage driver contributed to the accident, but the truck driver did not, Brouthers said. He said the truck belonged to Carolina Redi-Mix Co. of Summerville.

The Honda was nearly flattened on one side and the occupants were pinned inside.

"All the concrete came out, pouring onto the car and in the car," Rogers said. "It literally filled the car with concrete up to their waist."

The concrete began to dry as nearly 20 rescue workers used their hands and shovels to clear away the mixture, Rogers said. They had to cut the car away from the mother and her children, he said.

"If anybody comes out of it alive, it's a miracle," said Diane Turok, who was stuck in traffic along with hundreds of other afternoon commuters. Eastbound lanes were closed for nearly two hours while authorities worked to clear the scene. Rush-hour travelers avoiding the interstate were stuck in long lines of traffic along College Park Road and U.S. Highway 78.

Though the crash did not affect westbound lanes of the interstate, traffic was snarled as drivers slowed to watch the commotion.