Passengers on an Austrian train running from Bregenz to Vienna were shocked when they heard a recording of an Adolf Hitler speech play over the train's loudspeaker system on Sunday.

Nazi slogans such as "Heil Hitler" and "Sieg heil" were also heard via the train's intercom, according to several passengers on the train.

Vienna Rabbi Schlomo Hofmeister was on the train and said in a tweet that he was "shocked" after hearing Hitler's speech played and the train's failure to stop it immediately.

"DISTURBING I felt above all, when some passengers began to laugh, when the voice of Hitler & the words "Sieg Heil!" boomed from the loudspeakers and the train didn't provide any explanation or reassurance, but all this was ignored!," Hofmeister wrote.

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.

The spokesperson said the incident has been reported to the Austrian police and they are investigating.

Two people allegedly involved in carrying it out were identified from the train's video surveillance.

"It is absolutely clear that any abuse should be punished, especially the illegal use of Nazi symbols is absolutely unacceptable," the spokesperson added.

'Completely helpless'

After hearing the broadcast of Hitler's speech, David Stögmüller, member of Austria's upper house of parliament, tweeted a video of himself expressing disbelief.

Stögmüller recorded the last bit of the Hitler announcement, with a voice saying the Nazi slogan "Sieg heil" could be heard in the background.

He wrote that a train attendant was "completely helpless" after "Sieg Heil" could be heard several times. He called for "a report and quick clarification."

Journalist Colette Schmidt, who was also on the train, asked for an explanation in a tweet on Sunday. "Could you please enlighten us as to why an entire train" heard Hitler's speech, she asked. "Including fervent Sieg Heil shouts? Have they been hacked? What's going on?," she wrote.

"Quite apart from the fact that I and other Austrians were completely shocked: what does a guest from abroad think when Hitler speeches are played over loudspeakers in our trains? Supposedly it came from "the technology". What?!," Schmidt said in the tweet.

Speaking to CNN, Schmidt said Hitler's speech was about 20 seconds long, followed by the Nazi slogans, and that the recording was on a loop.

The journalist said she was "frightened" after hearing Hitler's speech on the train.

"No conductor, no one came, there was no one to see. We were alone with this madness. "Who is driving this train now?" I asked myself," Schmidt said.

"It was very very scary," she added.