Five people have died and 40 others were injured after a Dutch tour bus slammed into a roadside crash barrier and overturned in eastern Switzerland.

Axar.az reports, citing The Associated Press, that the bus, with 45 people on board, overturned Thursday afternoon in a construction zone between the villages of Susch and Zernez in the Alpine canton of Graubuenden.

Seven rescue helicopters and 13 ambulance crews took part in the rush to evacuate the victims, police said. Three people remain in serious condition in the hospital.

Prosecutors and police were investigating what led to the accident, though no other vehicles were believed to be involved.