CHATTANOOGA, Tenn. — At least six people were killed and at least 23 children taken to the hospital after a school bus crashed into a tree Monday afternoon in Chattanooga, authorities said.

Hamilton County District Attorney Neal Pinkston told media outlets that five people died at the scene and one died at the hospital. Melydia Clewell, spokeswoman for the district attorney, confirmed the number.

Chattanooga Police Chief Fred Fletcher said early reports from investigators indicate the bus hit a utility pole before flipping over and wrapping around a tree in the Brainerd area of southeast Chattanooga.

"Certainly speed is being investigated very, very strongly as a factor in this crash," Fletcher said.

He said there were no obvious roadway conditions that appeared to have led to the crash and that police are still investigating whether alcohol played a role.

Fletcher described the crash as "every public safety professional's worst nightmare."

The National Transportation Safety Board tweeted Monday night that a "Go Team" of investigators would deploy to the accident scene Tuesday morning.

The Chattanooga Police Department did not confirm the exact number of dead.

The bus driver was being questioned and was cooperating with authorities, police said. The bus is operated by Durham School Services, according to spokesperson Carina Noble.

In a news conference Monday, Assistant Chief Tracy Arnold said there were 35 students from Woodmore Elementary School on the bus ranging from kindergarten through fifth grade.

Rescue crews worked until after dark. Nearly an hour after the crash, two bloodied students remained on stretchers in a nearby front yard, the Chattanooga Times Free Press reported. Others who did not go to the hospital walked away clutching their parents’ hands, the Times Free Press reported.

Images posted on social media also showed interim Hamilton County Schools Superintendent Kirk Kelly racing to the scene of the crash.

And blood donors rushed to Blood Assurance in downtown Chattanooga, where marketing coordinator Mindy Quinn said there was a line out the door.

The fire department described the crash scene on Twitter as "very serious" and Chattanooga's mayor called it "horrible."

This was the second bus crash in Tennessee in recent days involving dozens of students.

Nearly two dozen Chester County Beta Club students on their way to a convention at Gaylord Opryland were injured Friday morning in a crash after a school bus flipped on Interstate 65 in Nashville.

None of those injuries were life-threatening.

The governor said events like Monday’s and last week’s crash in Nashville could lead officials to begin additional talks about safety.

“To me it’s a good discussion to have,” Haslam said. “I think when this is over it’s time to have a good conversation about everything around school buses.”

Nationally, from 2004 to 2013, U.S. drivers were involved in 340,039 fatal motor vehicle traffic crashes, according to the National Highway Traffic Safety Administration(NHTSA). Of those, 1,214, or just .4%, were classified as "school-transportation-related," involving a school bus or other vehicle functioning as a school bus that was transporting children to or from school or related activities, such as sports or field trips.

Kelly said schools will be open tomorrow, and Woodmore will have guidance counselors and other support available for students and staff, according to the Chattanooga Times Free Press.

"This has been a great tragedy for us," Kelly said. "We have suffered a great loss today ... one of the worst days we've had in our school community."