Austrian officials say a bus carrying Ukrainian tourists crashed through a guardrail while approaching a highway and flipped, injuring 11 people, two of them seriously.

Firefighter spokesman Franz Resperger said the pre-dawn accident occurred Monday on a ramp leading to the main highway connecting Austria and Hungary near the town of Schwechat, east of Vienna.

Police are still investigating, but he says it appears to have been caused either by the driver losing control on a curve or falling asleep.

The bus was carrying 14 people. Red Cross officials say all 11 injured have been hospitalized.