GENEVA (AP) — Police say 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.

The bus, with 45 people on board, overturned Thursday afternoon between the villages of Susch and Zernez in the Alpine canton of Graubuenden.

Three people remained in serious condition at hospital, police said.

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

Oad, a travel agency behind the trip, said in a statement that it was “deeply shocked and devastated by the tragic bus accident” and its thoughts were with those involved and their loved ones.

Swiss President Guy Parmelin, writing on X, vowed that Swiss authorities would ensure a “comprehensive and thorough investigation” of the case.

Images from the scene showed crews in fluorescent suits cutting into the overturned bus with power saws overnight, as police looked on.