Image copyright AP Image caption School bus driver Johnthony Walker was arrested early on Tuesday morning

Police in Tennessee have arrested the driver of a school bus that crashed on Monday, killing at least five children and seriously hurting several more.

Chattanooga Police charged 24-year-old Johnthony Walker overnight with five counts of vehicular homicide, as well as reckless driving and endangerment.

There were 37 children on board when the bus swerved off the road, striking a tree and a utility pole.

Federal officials have arrived in Tennessee to assist the investigation.

On Monday evening police said that five children had died and more than 20 had been injured.

Hamilton County District Attorney Neal Pinkston said that a sixth child had later died in hospital, but that could not be immediately confirmed.

A police affidavit posted on Chattanooga station WTVC says that Mr Walker was driving well above the 30mph (48km/h) speed limit when the crash occurred. No other vehicle was involved.

Emergency crews took nearly two hours to get all the children off the bus. Many lay bleeding on stretchers, while others walked away stunned and in shock with their parents.

School officials quoted by the Chattanooga Times Free Press said that 12 children remained hospitalised on Tuesday, with six in intensive care.

Image copyright AP Image caption The bus was taken away from the scene of the accident on Tuesday

Image copyright Chattanooga Fire Dept Image caption Police said the crash was "every public safety professional's worst nightmare"

Roads at the time "appeared to be clear and dry", officials said at a Monday afternoon press conference.

They added that Mr Walker had been co-operating in the investigation, and that a warrant had been issued to remove the bus's black box, which records data about the vehicle's movement.

The parent of two children who were aboard the bus told ABC News on Tuesday morning that he had sometimes seen the driver going faster than he should be.

"There has been times where I've seen him going a little faster than he probably should be going," Craig Harris told the programme, adding that his two children are in shock and pain but are getting better.

Image copyright AP Image caption Flowers are laid at a makeshift memorial at Woodmere Elementary School

Chattanooga Mayor Andy Berke said the "most unnatural thing in the world is for a parent to mourn the loss of a child".

"There are no words that can bring comfort to a mother or a father. So today, the city is praying for these families," he said.

The Woodmere Elementary School opened on Tuesday, with grief counsellors available to students, officials said.

Local blood banks have asked that people schedule appointments, as there have been long queues since Monday afternoon of people wishing to donate blood.

Mr Walker's bond has been set at $107,500 (£87,000) and he is due in court later this month, court records show.