(changes dateline, releads, updates with arrest of bus driver, includes latest injury figures)
The driver of the bus that crashed Monday near the central Spanish city of Avila was arrested following the accident, which killed nine people and injured 22 others, officials said.
The 54-year-old driver, whose name was not released, was arrested for falling asleep at the wheel, Interior Minister Jorge Fernandez Diaz said in a press conference.
Six of the 22 people injured in the crash are listed in serious condition, officials said.
The driver, who was not injured in the accident, admitted that he fell asleep, investigators told Efe.
The man tested negative for alcohol and drugs, investigators said.
The bus driver was arrested on manslaughter and negligence charges.
The 16-year-old bus went off the highway about six kilometers (3.7 miles) from Avila and hit a guardrail, but it never flipped over.
The bus was about 75 percent full at the time of the accident, passengers told Efe. EFE