Journalist Suki Kim went undercover in North Korea as a teacher at the prestigious Pyongyang University of Science and Technology in 2011 and discovered a world bound in secrecy, surveillance and lies.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Listen Duration: 6 minutes 5 seconds 6 m Listen to Mark Colvin's report. Download 11.2 MB

Students at the elite school were confined to a campus that was guarded by the military and watched by minders at all times.

"None of us were allowed out of the campus, students were never allowed out, the teachers were only allowed out with a minder to only look at Great Leader monuments," Ms Kim told Mark Colvin from the ABC's PM program.

"We grew really attached because I spent all my time with them, and what that also meant was there was a great empathy for the predicament they were in."

Ms Kim penned a memoir about her time in the hermit kingdom, documenting a tightly controlled and repressive place where even the most basic information was kept from the students.

"Their knowledge is incredibly limited — only about the Great Leader — and also everybody's watching everyone, so even if they did know some things that they're not supposed to know, they can't ever show it," she said.

North Korean girls outside Kumsusan Palace where Kim Il-sung is embalmed, 2011. ( Suki Kim )

Ms Kim said at times students let on that they knew about aspects of life outside of North Korea, but it only ever came to light by accident.

She recalls a time when one student let slip that he loved to sing rock and roll songs and froze in terror.

"He just stopped," Ms Kim said.

"He just lowered his face and he looked around instantly to see who might have heard him because there everybody's watching everyone.

"And the pure fear that I saw on his face ... I mean it was just [and] instant reaction.

"And all that was, was just a 19-year-old boy listening to rock and roll and it was that little slip — how can you even consider that a slip — but normally they're supposed to say they only sing songs about the Great Leader or about friendship."

Students doing morning exercises, 2011 ( Suki Kim )

Ms Kim was surprised to discover her students had heard of Harry Potter, but showing them the film only highlighted how disconnected they were from the rest of the world.

"I'd been teaching essay writing to my students, which ended up being really impossible because essays are about actually coming up with your own argument and proving it with evidence, which is critical thinking, and they really couldn't do it, so essays became this headache classroom lesson," she said.

"And in that movie, Harry Potter, there's a scene where Hermione says 'I have to write an essay for Professor Snape's class' and she rolls her eyes, and they realised that she also didn't like writing essays.

"And my students really connected with that moment ... they couldn't believe there was a girl outside, in the outside world, who also was writing essays.

"So I think that moment was really special and also heartbreaking for me, realising that's what they really want, as 19-year-old kids, to connect with the outside world, which their country will never let them."

Top students kept from accessing internet

The school authorities tried to give Ms Kim the impression students had access to the internet, but in reality it was more akin to an internal intranet.

"The school even tried to make us think that some students were on the internet by showing us 10 students sitting in front of a computer with a Google page open, but then when you talked to them, they had no idea what the internet was," she said.

"And these were the students of science and technology — in 2011 they did not know the existence of the internet."

She also found the students lied constantly and easily.

"For example, they'll say they called home all the time for example with their family, and I knew for a fact they were not allowed to keep in touch with their family," Ms Kim said.

Students on a snowy day after an exam; Kim Jong-il's death would be announced just a few days later, 2011 ( Suki Kim )

"Or they'll tell me that they cloned a rabbit when they were a fifth grader, which is completely impossible."

Ms Kim said it was unclear whether the students knew the difference between truth and lies.

"They get told so many insane things about the greatness of their nation and even their own past in a way, to show what great students they are, how advanced they are to the rest of the world, and part of them were just regurgitating this because that's all they've ever been taught," she said.

"At times I wondered if they didn't know the difference between lies and truth because when you think about it, their entire world is built on lies."

Her students will be in their early 20s now and Ms Kim said she still worried for their future.

"Most of all them come across completely loyal to their regime in the book, so on that front I'm not worried," she said.

"I am more, I guess, concerned because they live where they live and their new leader is not even remotely better than their other leader.

"So as long as the system of the Great Leader is intact I would always worry about them."