CHATTANOOGA, Tenn. -- Bloodied students lay on stretchers, while other children walked away dazed with their parents after an elementary school bus crash that killed six Monday in Chattanooga.

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

Police said the ages of the students ranged from kindergarten through fifth grade.

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Chattanooga Police Chief Fred Fletcher said 35 students were on board on the bus when it crashed, according toCBS Chattanooga affiliate WDEF. At a news conference, Fletcher said that the bus was the only vehicle involved.

Fletcher said the crash was “every public safety professional’s worst nightmare.”

Fletcher said police were interviewing the bus driver to determine what happened and told reporters later that investigators were looking at speed “very, very strongly” as a factor. The bus was the only vehicle involved but the crash scene covers a significant area, he said.

The Chattanooga Fire Department’s Public Information Director, Bruce Garner, said in a tweet that 23 patients were taken to hospitals in ambulances.

Colonel Tracy Trott of the Tennessee Highway Patrol tweeted that children were both killed and injured:

My heart goes out to the families of the children that were killed & injured in the school bus crash in Chattanooga this evening. TT — Colonel THP (@THP_Colonel) November 21, 2016

The police department said the bus driver is cooperating in the investigation.

“We just wanted to inform you that Hamilton County schools faced a great tragedy today,” read a text message sent to parents in Tennessee’s Hamilton County on Monday, according to WDEF. “School and county personnel are on scene of a bus accident on Tally Road in Chattanooga. Extra counselors and support staff will be on hand to help students process this horrible incident.”

The NTSB said Monday evening they will send a team to investigate.

NTSB launching Go Team to investigate school bus crash in Chattanooga, TN. Team to deploy a.m. of Tuesday, 22 Nov. — NTSB_Newsroom (@NTSB_Newsroom) November 22, 2016

Shocking pictures posted to social media from the scene of the accident showed a tree slicing through the crashed school bus.

Last patient just extricated from bus by #ChattFire here at school bus crash on Talley Rd. EMS is transporting. pic.twitter.com/0GhrSSy0Wc — Chattanooga FireDept (@ChattFireDept) November 21, 2016

Governor Bill Haslam issued a statement on the deadly bus crash.

“Our thoughts and prayers are with victims of today’s tragic school bus crash in Chattanooga,” the statement said. “It’s always a very sad situation when you have a school bus crash with children involved and we will do everything we can to assist the local authorities and the victims’ families.”

Transportation company Durham School Services confirmed that its bus was involved in the crash and said it could not answer questions at this time due to the active investigation.

JUST IN: statement from Durham, that operates the bus pic.twitter.com/PQuecuMxBd — Latricia Thomas (@LatriciaTnc9) November 22, 2016