VICTORIA, Texas -- Driver fatigue may be to blame for a tour bus wreck that killed one man and injured nearly four dozen others on Wednesday, officials told KPRC Local 2.

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Slideshow: Deadly Tour Bus Crash Near Victoria

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The Victoria County Fire Marshal's Office said the bus flipped on its right side at 4:15 a.m. on Highway 77 near U.S. Highway 59, a few miles south of Victoria.

The bus blocked all lanes of Highway 77. Investigators said it was dark and the driver of a pickup truck did not notice the wreckage before he slammed into the overturned bus.

"(It was) dark around. The bus was lying down with the black part in front of me and I hit it with my truck," driver Aurelio Melchor said. "No lights, no nothing. No people out, not nobody."

Melchor said he could not see the bus and the passengers on the bus probably could not see him, either.

"Probably, everyone was sleeping. Nobody knows what happened," he said.

"The investigation is centering on driver fatigue," Department of Public Safety spokesman Tom Vinger said. "It looks like he ran off the road, way overcorrected then tipped over on the passenger side."

Weather did not play a role in the wreck, Vinger said.

Pedro Mendez, a 55-year-old passenger on the bus from Houston, died at the scene.

Officials said 46 people were taken to area hospitals with a variety of injuries, including broken bones, a broken neck and a woman whose arm was amputated. Melchor was not hurt.

Francisco Cardenas, 66, said he was asleep while returning from the holidays in Monterrey when he woke to the screams of people as the bus turned on its side.

"The hardest thing was to see all the other people," said Cardenas, who returned to Houston later Wednesday with a cut on his face, blood on his shirt and blood on his shoes. "There was no way out."

He said people eventually pushed the emergency exit on the roof to escape.

David Santos, 53, of Houston, said the bus wasn't speeding, but he felt the driver lose control then overcorrect. Santos said he saw one woman whose head was stuck under the bus.

DeTar Healthcare System in Victoria, located about 125 miles southeast of Houston, took 22 passengers, said spokeswoman Judith Barefield. Of those, one was in critical condition, one was transferred to another hospital outside Victoria for a "higher level of treatment," two were in serious condition, 11 were in fair condition and seven were treated and released, she said.

Another 24 people were brought to Citizens Medical Center in Victoria, said spokeswoman Shannon Spree. Of those, one was airlifted to Brooke Army Medical Center in San Antonio and two were airlifted to Wilford Hall Medical Center in San Antonio, she said. One of those airlifted had a severe head injury, she said.

Nine others were admitted to Citizens Medical Center, two in intensive care. The other 12 were treated and released or being treated, Spree said. She said three or four of the passengers had broken backs and that a lot of them had orthopedic injuries such as broken collar bones and arm injuries.

San Antonio's University Hospital had received one minor patient in critical condition, said spokeswoman Dora Quiroga.

Wilford Hall Medical Center spokeswoman Sue Campbell confirmed that two patients were transported there. She said they were in surgery and their conditions were unknown. One person was at Brooke Army Medical Center in stable condition, said medical center spokesman Dewey Mitchell. Another person originally came to BAMC and was transferred to University Hospital, he said.

The bus was operated by Capricorn Bus Lines Inc. in Houston. Francisca Flores, manager of the family-owned bus company, said this is the first wreck in the nine years since Capricorn began.

"We don't really have accidents," she said. "We have good drivers."

The company has four buses and only makes trips between Houston and Monterrey, she said. The trips are nine to 10 hours long each.

The bus left Monterrey at about 7:30 p.m. Tuesday and stopped in Laredo at 10:30 p.m. for 90 minutes.

Worried relatives went to the bus line's headquarters on Airline Drive in Houston looking for answers.

"We don't know nothing," said Julio Rodriguez.

Rodriguez said his grandparents were on the bus. They travel between Houston and Monterrey several times a year.

"We're terrified," he said.

Rodriguez said his grandparents were on board during another wreck a few years ago.

"They got into an accident like two years ago or three," he said.

Some of the passengers were expected to return to Houston on Wednesday afternoon. Flores said she did not know how many people were going to be able to make the trip.

"Another bus company is going to help us," Flores said.

Vinger said the driver wasn't seriously injured, and that it's too early to tell whether he'll face charges. Company officials said there was only one driver on the bus.