CHATTANOOGA, Tenn. — A school bus driver was behind bars Tuesday after a crash killed five youngsters and plunged Chattanooga into mourning over what the mayor called the “most unnatural thing in the world” — a parent losing a child.

Police said Johnthony Walker, 24, was speeding along a narrow, winding road Monday afternoon with 35 elementary school students aboard when he wrapped the bus around a tree.

Walker was arrested and charged with five counts of vehicular homicide.

Chattanoogans lined up to donate blood, created a memorial of flowers and stuffed toys at the crash site and held a prayer vigil. Parents who send their children to school every day struggled to come to grips with the shock and break the news to their loved ones.

“It's real tough," said Dujuan Butchee, whose daughters, Jamya and Janesa, are eighth-graders who used to go to the same school as the youngsters killed in the wreck. “It's tough on my kids because they know some of the victims as well.”

Police said Walker was driving well over the posted 30 mph limit when he lost control of the bus. He was jailed on $107,500 bail for a court appearance Nov. 29 on charges that also included reckless driving and reckless endangerment.

Twelve children remained hospitalized Tuesday, six in intensive care, said Kirk Kelly, interim school superintendent.

Three of the children killed were in fourth grade, one was in first grade and another in kindergarten, Kelly said. Their families were notified, but their names were not released. All the children went to Woodmore Elementary.

“The most unnatural thing in the world is for a parent to mourn the loss of a child,” Mayor Andy Berke said. “There are no words that can bring comfort to a mother or a father. So today, the city is praying for these families.”

Armanie Bryant, a Chattanooga middle-schooler, said: “They didn't get to live their lives. They didn't get married. They didn't have no kids, anything about their future.”

The National Transportation Safety Board sent a team to investigate, and police obtained a warrant to remove the bus' black box, which contains data on the vehicle's movements.

Walker had an accident involving property damage in September, and his license was suspended for about a month in 2014 for failure to show proof of insurance, according to state commercial driver records. He appeared to have no criminal record in Tennessee, authorities said.

Hamilton County School District spokeswoman Amy Kutcher declined to say whether the district had received any complaints involving Walker, who was employed by an outside bus contractor, Durham School Services. She referred all questions about his performance and that of other Durham drivers to the company.

Durham CEO David A. Duke issued a statement on Twitter saying the company was “devastated” by the accident and working with police and school officials to investigate.

Durham, based in Warrenville, Ill., operates 13,700 vehicles around the country and has nearly as many drivers, according to the Federal Motor Carrier Safety Administration. It had a “satisfactory” safety rating from the agency in July 2015.