Breaking news from CNN.com

ATLANTA, Georgia (CNN) -- At least six people were killed when a charter bus carrying a college baseball team from Ohio fell from an overpass onto Interstate 75 early Friday in Atlanta, police said.

Twenty-two people were injured, including three critically, hospital officials said. There were 35 people on the bus, Atlanta police spokesman Joe Cobb said.

Nineteen students were taken to Grady Memorial Hospital, the city's trauma center, where three were in critical condition, Grady officials said. (Watch as a police spokesman describes the "walking wounded" )

Dr. Leon Haley, Grady's director of trauma services, said two of the 19 students had been taken to surgery. Another student, in critical condition, was awaiting a bed in the intensive care unit. The injuries for the other 16 were mild to moderate, Haley said.

Officials at Piedmont Hospital said three people had been brought to the emergency room with "slight" injuries.

The crash occurred just before dawn north of downtown Atlanta.

The bus exited I-75 southbound in an HOV lane in the center of the highway that leads onto a bridge at Northside Drive. The bus apparently did not stop at the top of the exit ramp and plunged off the bridge onto the southbound lanes of the expressway, according to two drivers, whose vehicles were hit by the bus or debris falling off it. (Watch as police explain how confusion over the HOV lane and exit may have led to the crash )

An Atlanta Journal-Constitution reporter said he saw the wreck during his morning commute and initially thought it was a jack-knifed tractor-trailer before realizing it was a bus.

"There were young people crawling out of the bus. I just tried to help them as best I could," Mike Morris said.

The bus was carrying members of the Bluffton University baseball team, which according to its Web site, was scheduled to play Eastern Mennonite University on Saturday in Sarasota, Florida, before heading to a tournament in Fort Myers, Florida.

Bluffton University is a Mennonite Church USA affiliated-school south of Toledo, Ohio.

"The fact that they're young men, athletes will certainly help them in the long run," Grady's Haley said. "... From a starting point, they're all pretty good."

Haley added that "they're pretty calm, they're asking the appropriate questions. ... They're very aware of what's going on."

Aerial footage from the scene showed a mangled barrier fence on the bridge above the bus. Debris and luggage were scattered around the bus, and at least nine fire trucks were at the scene.

Georgia Department of Transportation cameras showed the bus lying on its side in the southbound lane of the expressway. Firefighters surrounded the bus.

The wreck closed I-75 in both directions, snarling morning rush-hour traffic, police said. Police later re-opened the northbound lanes. Rescuers later brought the bus upright, and it was taken away from the scene.

James Grandey, the father of the team's coach, said his son, also named James, sustained injuries to one of his legs. The senior Grandey was interviewed by telephone from his home in Ohio.

The National Transportation Safety Board said it would investigate the crash because it involved a charter bus.