Nazi slogans such as “Heil Hitler” and “Sieg heil” were also heard via the train’s intercom, according to several passengers on the train, reports CNN.

Vienna Rabbi Schlomo Hofmeister was traveling in the same train and said he felt 'disturbing' to listein to the loudspeaker recording.

 "I found DISTURBING v. a., when some passengers started to laugh, when Hitler's voice & the words "Sieg Heil!" boomed out of the loudspeakers & no explanation or reassurance was given by the train, but everything was ignored!" he tweeted.

About 25 minutes before arriving in Vienna, in the city of St. Pölten, Hofmeister said it all began with “strange music, snippets of conversation and laughter which suddenly turned into a Hitler speech played louder and louder,” the Rabbi told CNN on Monday.

At first, he thought it was a mistake, then a bad joke, and “suddenly he felt queasy” because it was unclear whether only the public address system or even the entire train had been hijacked. Some of the other passengers panicked, others laughed at the embarrassment, he recalled.

“Someone has illegally opened the intercom with a duplicate key and played a Hitler speech over a loudspeaker,” a spokesperson for the rail operator ÖBB told CNN on Monday.

An investigation into the incident has been started.