Updated 12:12 p.m. ET
(CBS/AP) LITCHFIELD, Ill. - As a Megabus slammed into a bridge support pillar on an interstate highway in Illinois, the impact was so powerful that it flung 16-year-old passenger Baysha Collins from the upper-level seat where she was resting to a stairway leading to the lower level.
From there, she heard moaning from her fellow passengers on the double-decker bus, the front end of which was so mangled from the collision that emergency crews had to use ladders to rescue those trapped inside. At least one passenger was killed and dozens of others were hospitalized following the Thursday crash, authorities said.
"There was a lot of screaming and crying," said Collins, of Minneapolis, who was on her way to St. Louis to visit relatives. "There was blood everywhere. I was just in shock."
Passenger Zaq Hall told CBS Radio Chicago station WBBM he heard a tire blow out.
"And I knew what (that) sounded like because on my ride up to Chicago two days ago (from Kansas City), there was a tire that went on that bus also. Same front tire," Hall said.
Hall said it was "a really huge collision, and when I kind of came to my senses, I looked around and it was horrible. There were people in the aisles, laying there. Most people had some sort of blood on their face. It was pretty intense."
Trooper Doug Francis said it wasn't immediately clear what caused the crash and that he couldn't confirm there was a blown tire.
Aditi R. Avhad, 25, a native of India, was killed in the crash, Illinois State Police Trooper Brad Lemarr said late Thursday. The University of Missouri confirmed she was a graduate student there studying health administration.
At least 38 people -- nearly half of those on the bus -- were taken to hospitals or trauma centers, at least five of whom were transported by helicopter, Francis said.
Megabus spokeswoman Amanda Byers said the bus was at full capacity, carrying 81 passengers, when it crashed near Litchfield, about 55 miles northeast of St. Louis. It left from Chicago and was to stop in St. Louis and Columbia, Mo., before arriving in Kansas City, Mo.
Collins, who was among the three-dozen passengers taken from a crash site to a community center in Litchfield, said she first heard a "big boom," as if the wheel was skidding.
"It felt like the bus was going to tip over," she said.
A strong thunderstorm rolled through the area about four hours after the crash. Francis said the rain did not complicate the rescue and recovery effort, although it did make the crash reconstruction more difficult.
The National Highway Traffic Safety Administration said in statements that it was aware of the accident and would work with local authorities "to determine if there are safety implications that merit agency action," but that the agency was not investigating the crash.
Janis Johns, transportation director of Litchfield Community Unit School District 12, said the passengers were either uninjured or mildly injured and included some children.
By evening, many of the uninjured passengers already had been taken by bus from the community center to St. Louis. Others were picked up by relatives, including 27-year-old Megan Arns of St. Charles, Mo., a St. Louis suburb. Her parents made the 70-mile trip to get her.
Arns was on the top deck of the bus near the back talking to a woman next to her when "all of a sudden it felt like the bus ran over something really, really big." She said she could feel the bus lose control as it rolled into the median and toward the pillar.
"Absolute panic. People were screaming," said Arns, who got away with just a scrape on her head.
Arns and 22-year-old Enrique Villaroel of Chicago said passengers began helping each other almost immediately after the wreck.
"Panic at first, then total calm," Villaroel said. "Some people were carrying other people off the bus."
Villaroel said he also was on the upper level of the bus sleeping when he was awakened by screams. "I flew out of my seat and a little girl flew past me," he said, adding that the child appeared to be OK and he escaped with a few bruises.
A string of crashes involving low-fare buses in recent years have prompted calls for tougher regulation. Four passengers were killed in September 2010 when the driver of a double-decker Megabus smashed into a low bridge outside downtown Syracuse, N.Y. The driver was acquitted earlier this year of homicide in the deaths.
Fifteen people were killed in May 2011 when a bus swerved off Interstate 95 in New York City and was sliced in two. Two days later, another bus drove off the New Jersey Turnpike and struck a bridge support, killing the driver and passenger.