GENEVA – Switzerland’s popular Glacier Express tourist train derailed Friday in the Alps, killing one person and injuring 42 others on its spectacular journey between Zermatt and St. Moritz.

Police said 12 of the injured were in serious condition and most of the passengers were Japanese tourists. Police declined to identify the person who died.

Rail interruptions, let alone accidents, are rare in Switzerland. The Glacier Express — dubbed the “slowest express train in the world” — is known as much for its majestic mountain climbs as for its pedestrian 18 mph average speed.

Valais authorities said two of the train cars drove off the tracks and a third tipped over, but the cause of the accident wasn’t immediately known.

The three cars were at the back of the train and the derailment took place near the town of Fiesch and the mouth of the Aletsch glacier, Europe’s largest icemass.

Rail traffic remained closed near the accident site Friday evening and local police were investigating.

The 80-year-old Glacier Express runs several times a day all year round, carrying some 250,000 passengers a year.

It starts in Zermatt, at the base of Switzerland’s iconic Matterhorn mountain, and rumbles through terrain over a mile above sea level, surrounded by many of the highest Alpine peaks.

After 7 1/2 hours, 291 bridges and 91 tunnels, it ends in St. Moritz — one of the world’s ritziest winter resorts. Train cars have special large windows that sweep high onto the roof so tourists can take in the vast mountain vistas.

A celebration of Swiss engineering, the Glacier Express offers breathtaking views of mountains, glaciers, viaducts across rushing streams and switchback rail lines that sometimes go in full circles to spiral up or down the steepest slopes.

The accident was the country’s worst rail mishap since 2006, when three men died after a runaway train traveled for miles without brakes before crashing into another train.