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(CNN) — A pregnant woman woman who survived the New Mexico bus crash that killed eight people gave birth to twins hours afterward, hospital officials told CNN Friday.

The two children were born at Rehoboth McKinley Christian Health Care Services clinic in Gallup. They were then transferred to the neonatal intensive care unit at the University of New Mexico Hospital in Albuquerque, Sonlee West, a surgeon and director of the hospital’s trauma unit, said Friday.

West said the children were in critical condition.

The mother’s name and condition were not available. Authorities have only released the identity of one person involved in the crash.

Bus driver Luis Alvarez, 49, of Santa Teresa, New Mexico, was among those killed. The other fatalities will not be identified until next of kin have been notified.

The crash happened around 12:30 p.m. Thursday on I-40 between Gallup and Grants, after a tire blew out on the front driver’s side of the eastbound truck, the New Mexico State Police said.

The “80-thousand pound projectile” crossed the dirt median, jackknifed and collided head-on with the westbound bus carrying 48 passengers and the driver, New Mexico State Police Chief Pete Kassetas said Friday at a news conference.

The violence of the impact scattered bus parts and boxes of produce, and shut down the interstate for eight hours, Kassetas said. The number of injured people overwhelmed local authorities, who ran out of ambulances, he said.

Including the pregnant women, 26 people were taken to area hospitals for treatment, with one of them dying at a hospital, Kassetas said.

Five children were hurt and survived, he said. Fifteen people were unhurt.

The 35-year-old unidentified truck driver was not badly injured, Kassetas said.

When asked whether charges could be filed in the crash, Kassetas said: “There could be an expectation of charges depending on the outcome of the investigation. Equipment failure itself is not a chargeable incident. There have to be other factors.”

The National Transportation Safety Board sent 10 investigators.

Commercial motor vehicles typically do not have a “black box,” but investigators are determining whether there are any type of recording devices on this particular vehicle, NTSB spokesperson Pete Kotowski said in a press conference.

The probable cause of the accident will not be released until the investigation is complete, Kotowski said. The final report on the crash could take from 12-24 months, he said.

Kassetas said the truck was owned by a Fresno, California, company and was carrying a load of produce to Memphis, Tennessee.

The Los Angeles-bound Greyhound bus had originally departed from St. Louis and had just made a stop in Albuquerque prior to the crash, the company said. The bus passengers were from St. Louis and Albuquerque, Kassetas said.

“Tragically, a number of people have lost their lives, including our driver, who had 27 years’ experience with Greyhound,” the bus company said in a statement Friday. “Our hearts are with all those affected by this incident. We are cooperating with local authorities and the NTSB to determine the cause of the event.”

A traveler who encountered the wreck, Marc Gonzales, said the scene was a “complete catastrophe,” with skid marks on the side of the road.

Passengers tried to climb out the bus windows and bystanders grabbed ladders from their vehicles to try to rescue them, he said.

“It’s by far one of the worst accidents I’ve encountered. … It was horrible,” Gonzales told KRQE. “You could tell that people were distressed, screams were coming from the bus,” he said.

Kassetas praised the helpful motorists, calling them “heroes.”

“For them to stop and get involved is incredible,” he said.