A landslide derailed a passenger train in the Swiss mountains on Wednesday sending one carriage plunging into a ravine, but it appeared that miraculously there had been no deaths.

Police said five people were seriously injured and six slightly hurt in the accident on the line between the upscale mountain resort of St. Moritz and the eastern city of Chur.

Two of those injured were Japanese citizens, while another was Australian and the rest were Swiss, police said.

Terrified passengers crowded into the rear of another carriage in a bid to prevent it from tipping over the edge.

"The train made an emergency stop in the middle of nowhere," passenger Stevens Bockor was quoted as saying by news website 20 Minutes.

"We all rushed to the back of the carriage to put all of our weight there, so that it didn't tip into the abyss," he said.

Photos in Swiss media showed one of the bright-red carriages lying precariously on the ravine's slope, some 10 metres (65 feet) from the track, its fall apparently blocked by the dense pine forest.

Another carriage remained perched on the edge of the track, half of it hanging over the ravine.

"There was a guardian angel travelling on that train," Stefan Engeler, head of regional company Rhaetische Bahn, told the Swiss news agency ATS.

The eight-carriage train derailed shortly after 12.30 pm (1030 GMT) on an isolated stretch of track in the forest near the picturesque village of Tiefencastel.

Rhaetische Bahn spokesman Simon Rageth told AFP that a landslide was to blame.

Regional police said the debris struck the train as it travelled between two of the many tunnels that are dotted along the line, which runs above the Albula River valley.

"At least three carriages were derailed. According to an initial count, five people were seriously injured and six lightly hurt," police said in a statement.

Four helicopters rushed to the scene, swiftly taking the injured to several hospitals.

Police said that around 180 rescue workers were scrambled to the site of the accident.

- Heavy rain -

"There were around 200 people on the train," police said, adding that those who were unhurt made their way down the line to Tiefencastel, where paramedics treated them for shock.

The line was likely to be closed for two days, police said.

Eastern Switzerland's Graubuenden region, where the accident occurred, has been lashed by heavy rain in recent days after having been largely spared the storms that hit other parts of the country last month.

The rain has made streams overflow and waterlogged the mountainsides -- a common cause of landslides.

Experts said that such slides are highly unpredictable, but that Switzerland's authorities kept constant watch.

In July, storms caused landslides that blocked several lines, including between the capital Bern and the western city of Fribourg, as well as from Montreux on the shores of Lake Geneva to the mountain town of Zweisimmen.

July's rain also flooded another line near Bern and forced the closure of several roads.

The Swiss are Europe's top rail users, and their network is envied abroad for safety and quality.

After an accident-free 2012, safety has again made headlines.

In July 2013, a head-on collision blamed on signal-jumping killed a driver and injured 25 people near Payerne in western Switzerland.

Wednesday's accident comes just two days after three Israeli tourists died and five were seriously injured when a train hit their minibus at an ungated level crossing in the central Swiss Alps.