Two female passengers were killed Tuesday morning when a Greyhound bus carrying 20 passengers flipped on its side in South San Jose, tying up traffic and raising questions about bus driver working conditions and hours.

In an afternoon news conference, California Highway Patrol Officer Chris Miceli said the driver – who was reportedly in stable condition at Regional Medical Center of San Jose – acknowledged he had been "fatigued."

The CHP identified the driver as 58-year-old Gary Bonslater of Victorville, California.

"He did say he was fatigued leading up to the collision," Miceli said of Bonslater. "He says he remembers hitting the black barrels and then the next thing he remembers the bus was on its side."

Passengers claim Bonslater seemed tired and report he was knodding off at the wheel.

Bonslater is a veteran driver who was hired by Greyhound 26 years ago. The CHP said Bonslater had a clean driving record prior to Tuesday's crash.

CHP Sgt. Lisa Brazil said in the collision two women were ejected from the windows and died at the scene. One woman killed in the crash has been identified by family members as 51-year-old Fely Olivera, who leaves behind two sons.

The accident was reported shortly before 6:40 a.m. on U.S. Highway 101 at state Route 85, a busy South Bay thoroughfare that remained jammed during the rainy, early-morning commute.

In addition, Brazil said that eight other people suffered injuries, including an 8-year-old boy and 72-year-old woman. One adult suffered major injuries, the CHP said. Initial reports were that all 18 passengers were injured.

#drivingtofast#greyhoundbus#fullofpeople#sanjose#california#accident A video posted by LIFE IS GOOD AND GOT BETTER (@harley_man1) on Jan 19, 2016 at 10:03am PST

"There were a few passengers having great difficulty dealing with what happened – the traumatic incident that occurred – but we were able to get them off scene and get them with their relatives and friends," CHP officer Amy Tritenbach said.

Witnesses driving behind the bus told CHP officers that they saw the rear end of the bus "fly in the air" while trying to veer into the carpool lane before flipping onto the K-rail, Brazil said.

She added investigators did not know why the bus landed on its side, and disputed reports from a passenger who told a news outlet that the driver may have fallen asleep.

Brazil said that all the passengers interviewed told officers that they were asleep themselves before the crash occurred. According to Greyhound's bus tracker, the vehicle had left from Los Angeles just before midnight. Its final destination was supposed to be Oakland. A CHP officer told NBC Bay Area the bus made a stop in Gilroy to let two people off.

The bus was also scheduled to make stops in Avenal, San Jose and San Francisco.

"We do apologize," Greyhound spokeswoman Lanesha Gipson said. "Safety is the cornerstone of our business."

She would not elaborate on any more details of the crash, saying it was under investigation.

Larry Hanley, president of the Amalgamated Transit Union, which represents Greyhound bus drivers, told NBC Bay Area he did not have firsthand knowledge of the accident early Tuesday morning.

But Hanley did say that the union has been pushing Congress to act to include bus drivers in the Fair Labor Standards Act.

On average, inter-city bus drivers earn about $13 an hour and can work 70 hours a week and they don’t get overtime past 40 hours, the union states. After every 10 hours, they must take a break, however.

According to the U.S. Department of Transportation, fatigue has contributed to about 3 percent of all fatal crashes nationwide since 2005, and 13 percent of all big rig and bus crashes were caused by driver fatigue in 2006 and 2007.

Lengthy shifts behind the wheel were also one of 2014's top violations for truckers and bus drivers, federal officials found.

Most drivers have multiple jobs and are often fatigued, he said. "There’s a crisis in America," Hanley said. "The bus industry is forcing drivers to work too many hours to make a living wage."

While Gipson wouldn't speculate on whether the bus driver had been fatigued or not, she did say that Greyhound mandates its drivers get "nine hours of rest" after each 10-hour shift.

The crash was horrifying to those who witnessed its aftermath.

Anthony Cordero was driving to his job in Palo Alto with his two children, ages 3 and 4, when he passed by the crash. He heard responders inside the emergency vehicles shouting, "Get out of the way! Move!"

He said he saw the bus "completely smashed" and "literally hanging" over the side of the concrete barrier. He was listening to the radio and knew that there were fatalities. He asked his children to look away.

"I feel really badly for the families involved," he said. "But I also feel thankful. I was running a little late. If I was running on time, I would have been in that lane."

CHP investigators spent the day measuring and inspecting the bus, taking photographs and checking the road for signs of skids. They said the bus was outfitted with a camera but couldn't confirm whether it was operating at the time of accident.

The National Transportation Safety Board says it also plans to investigate the deadly crash, which littered the highway with passengers' belongings, including blankets, a pillow and a shoe.

"Terrible as it is, the fact that no other vehicle was involved is miraculous," Miceli said.

The bus was uprighted by crews after 3 p.m. After being mounted on a truck, the crumpled bus was removed from the scene just after 5 p.m.

Greyhound passenger Robert Wesley, who was preparing for a ride from San Jose to Southern California Tuesday afternoon, said he was shaken by the news of the fatal crash, but didn’t plan to alter his travel plans.

"That’s really sad, really sad for those that lost their life," he said. "If it happened once it might happen again, but I’m not going to stop traveling just because of an accident."

There have been other notable bus fatalities in Northern California. Two years ago, 10 people were killed when a Fed Ex truck hit a bus carrying high school students en route to Humboldt State University. In 2009, five French tourists were killed when their charter bus left the road on Highway 101 near Soledad.

And the worst highway disaster in Bay Area history was when the brakes failed on a bus near the Benicia-Martinez Bridge, killing 27 Yuba City choir students and one teacher in 1976.

Friends and family of anyone who was on Greyhound bus No. 6876 can call 1-800-972-4583 to check on their status.

NBC Bay Area's Rhea Mahbubani and Kristofer Noceda contributed to this report.