Vienna  - A 10-year-old Czech boy was killed and 10 other passengers injured when their tour bus crashed in south-eastern Austria in the early morning hours Saturday, officials said.

The bus was carrying around 50 passengers, most of them schoolchildren from the northern Czech town of Zelezny Brod to a seaside resort in Croatia, Czech Consul in Vienna Milan Kovar said.

The victim was the son of one of the bus' two drivers. "The boy was not an official trip participant. His dad took him along," the consul said.

It was unclear whether the boy's father drove the bus on the motorway near the city of Gratz at the time of the accident.

The driver told the police that he swerved to the right to avoid a braking motorist. The bus then tipped onto its side on the highway's soft shoulder.

Ten passengers were taken to a hospital for treatment, the police said.

Contrary to early reports of several serious injuries, only one woman sustained medium-level injuries. She was awaiting transport from a Gratz hospital to the Czech Republic in a stabilized condition, the consul said.

The remaining nine passengers were injured lightly, he added.

The group decided to carry on with the school trip boarding a replacement bus en route to Croatia on Saturday afternoon. (dpa)