A tractor-trailer crossed a southern Oklahoma highway median and plowed into the side of a Texas college softball team's bus, killing four team members and injuring more than a dozen others, authorities said.

The collision involving the North Central Texas College team happened at around 9 p.m. Friday on Interstate 35 south of Davis, which is about 70 miles south of Oklahoma City and 60 miles north of Gainesville, Texas, where the school is located.

The team was heading home from a scrimmage earlier Friday against Southern Nazarene University, in Bethany.

"This is the most traumatic event that NCTC has had in its 90 years of history," College President Brent Wallace said at an emotional news conference Saturday in Gainesville, Texas, about 60 miles south of the crash site on Interstate 35.

The four players killed were identified by the Oklahoma Highway Patrol as Meagan Richardson, 19, Brooke Deckard, 20, Katelynn Woodlee, 18, and Jaiden Pelton 20. The women all were from small North Texas towns near the campus.

Three of the players died at the scene and a fourth died at a hospital in nearby Sulphur, Oklahoma, Highway Patrol Capt. Ronnie Hampton said.

Oklahoma University Medical Center clinical coordinator Darina Shellman said 18-year-old Bailey Buchanan was in critical condition Saturday. Kelly Wells, spokeswoman for Norman Regional Hospital, said 19-year-old Rachel Hitt was listed in fair condition.

The tragedy shocked the close-knit Texas community college of about 10,000 students. Rich Raymond, father of freshman player Emily Kuser, who survived the crash, said many of the girls had been playing together on regional softball travel teams since they were six or seven years old.

"It's just an amazing family of girls and athletes and coaches," Raymond said. "Just such a tight community. And even if your girl isn't going to the school there's a lot of pain right now."

It was not clear why the northbound 18-wheel tractor-trailer lurched across the median into the southbound lanes.

Hampton said the team's coach, who was driving the bus, declined treatment at the scene and escaped without serious injury. He said 15 other bus passengers were hurt, as was the driver of the tractor-trailer, who was expected to survive.

"Right now, it's being investigated like a homicide," Hampton said, adding that both drivers will undergo standard toxicology tests. Hampton said details of the crash were still not known but "something happened to cause (the semi-tractor driver) to depart the roadway and impact the other vehicle."

He said the accident will remain under investigation for several weeks.

"We have a lot of injuries, and a lot of death," he told FoxNews.com. "It's a tragic thing for everybody involved."

Hampton said the semi crossed the median and veered into the southbound lanes, hitting the bus.

"When it impacted the bus, it just kept going and went off the side of road. ... We knew we had a two-vehicle accident by what we saw at the scene. ... But it took about an hour before we found the semi," he said.

The front end of the team van was virtually untouched, but the sides of the vehicle were heavily damaged. Troopers and witnesses said the driver's side of the van sustained the worst damage.

A posting on the North Central Texas College Facebook page reads: "We ask for your prayers at this time for our softball team. Their bus has been involved in an accident in Oklahoma."

Southern Nazarene University sports information director David Noblett told The Oklahoman that North Central was scrimmaging SNU earlier Friday. The bus was returning to North Central Texas College, authorities said.

FoxNews.com's Karl de Vries and The Associated Press contributed to this report.