(CNN) -- The driver of a school bus that crashed, killing at least five children and injuring dozens, has been arrested, authorities in Chattanooga, Tennessee, said.
On Monday afternoon, a school bus carrying 35 students from Woodmore Elementary School slammed into a tree and split apart. Chattanooga Police Chief Fred Fletcher described the incident as "an absolute nightmare for this community."
At least five children died on the scene, said a spokeswoman from the Hamilton County District Attorney's Office.
The bus driver, Johnthony Walker, 24, has been charged with five counts of vehicular homicide, reckless endangerment and reckless driving. He could face more charges as the case proceeds to a Hamilton County Grand Jury, Fletcher said.
Walker has been cooperative and talking to investigators, police said.
Authorities received a call about the crash just before 3:30 p.m. Emergency officials worked for "many hours" to remove all the children from the bus, Fletcher said. Twenty-three victims were transported to Erlanger Hospital in Chattanooga and one was taken to another hospital, the chief said.
'We flipped over'
Fletcher said the bus, which was carrying students in kindergarten through fifth-grade, turned over on its side and struck the tree.
One of the children who was on the bus told CNN affiliate WDEF that the bus was traveling at high speed just before the crash. "He was going real fast and he hit a garbage bag," the boy said. "And we then hit a mailbox, then we flipped over and hit a tree real hard."
The children at the accident scene looked shell-shocked. Some were visibly injured and crying.
Distraught parents rushed to the site, searching for their kids. At the scene, parents were heard screaming, "That's my baby," CNN-affiliate WTVC reported.
Speed is a possible factor
The National Transportation Safety Board will send a team to Chattanooga early Tuesday, according to a tweet from the federal agency's account.
"Certainly, speed is being investigated very, very strongly as a factor in this crash," Fletcher said, adding that the investigation was still at an early stage.
He added that driving conditions were clear and dry. No other vehicles were involved in the crash.
Fletcher said "a warrant has been issued to remove the informational box on the school bus and review the video."
"Taking care of the children that are injured is our No. 1 priority. Taking care of the families who are looking for, caring for and grieving for children is our second priority," Fletcher said.
He added: "Our thoughts, our prayers and all of our efforts are with the families of these children and others impacted by this tragedy."
'A big boom'
A woman who lives near the crash told CNN affiliate WDEF the impact was so powerful it knocked her power out.
"I just heard a big boom," the woman said.
Fletcher, in a press conference, called the crash scene "a complicated crime scene" that covered a large area.
"What has happened today is every public safety official's absolute worst nightmare, but that is nothing in comparison to the nightmare that families and friends and our community is going through with this tragic loss to children in our community," Fletcher said.
A tweet from the Chattanooga Fire Department showed the bus on its side against a tree as emergency officials extricated the last patient through the back door.
Tennessee Sen. Bob Corker called the crash "heartbreaking" in a tweet.
'Hundreds and hundreds' of donors giving blood
Blood Assurance, a local blood bank, extended its hours at three locations, as "hundreds and hundreds" of donors flocked to give blood to treat crash victims, said spokeswoman Mindy Quinn.
"We have had people who were refusing to leave until they give blood," Quinn said.
She said they were fast-tracking O-negative donors and trying to schedule donors for the days ahead and into next week.
Interim Hamilton County Department of Education Superintendent Kirk Kelly called the crash "one of the worst days" the school community has experienced.
"This has been a great tragedy for us. We have suffered a great loss today," Kelly said in a news conference.
He said district schools will be open Tuesday, and officials will offer support for students and staff, including guidance counselors, for as long as they are needed.
"We will do everything that we can to try to help the families involved in this tragedy," Kelly said.