Korean Australians awoke in disbelief to the news that martial law had been declared — and swiftly revoked — in their home country overnight.

"This is unbelievable and very poor judgement of the president," said Jay Song, an associate professor from Australian National University.

"This is just embarrassing.

"What is he thinking? You know, this is the 21st century. Korea is a democracy."

The shocking development was a short-lived reality.

Some 155 minutes after embattled conservative South Korean President Yoon Suk Yeol declared martial law, parliamentarians voted against the measure.

Mr Yoon backflipped soon after — but observers say his political career is tarnished beyond repair.

For many, the turn of events was "surreal". Some had to check it was real and not "fake news".

For members of the Korean diaspora in Australia, the events evoked memories of a dark past.

The last time South Korea lived under martial law was more than 40 years ago.

In 1980, dictator Chun Doo-hwan instigated a deadly military crackdown against students and pro-democracy activists in the southern city of Gwangju, killing around 200 people.

Gil-Soo Han, from Monash University, vividly remembers living under martial law in the capital at that time.

"Around four o'clock or five o'clock in the afternoon, the whole world goes dead silent," he said.

"[People] can't move around, because those armies can kill the civilians — shoot to death at any moment. So it was really scary."

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Martial law harks back to military dictatorship

Sung-Ae Lee, an expert in Korean popular culture at Macquarie University, recalls being a student when martial law was declared in 1979 — when dictator Park Chung-hee was assassinated by his spy chief — and 1980 during the Gwangju massacre.

"At that moment, there was martial law, and then we couldn't go to the university at all … the soldiers were surrounding the gates."

She recalled attending a demonstration of thousands of people. When one young woman stood up to address the crowd, she was taken away by plain-clothes military personnel.

"She couldn't even finish her sentence … [before they] dragged her down," she said.

"I think they gave an injection to her [to sedate her] in front of us — 8,000 people. That was really a shock."

She said it was common for young people who looked like university students to be arrested without a warrant, and strict censorship meant many were kept in the dark about the brutality of the Gwangju crackdown.

"We were not aware of what kind of freedoms were allowed to us," she said.

"Freedom of speech was really restrictive. So you do not know who to believe, who to trust.

'It's a really sad history."

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She left the country in 1981 to study in the United States before relocating to Australia.

"I remember when I came to Australia after that, my father told me: 'Getting out of this country is success,'" she said.

For her, Mr Yoon's actions recalled South Korea's troubled past.

"I think he's very anachronistic," she said.

"History repeats itself."

Gil-Soo Han, from Monash University, said even before the martial law declaration, there was a petition circulating among diaspora academics imploring Mr Yoon to stand down.

Swirling political scandals, including surrounding Mr Yoon's wife and mother-in-law, had built significant pressure, he said.

"It's like a big mouse being really pushed and pushed into a corner, and he didn't know where to run, and then he did something just unimaginable."

What's North Korea got to do with it? 

When Sung-Young Kim first heard the news over breakfast, he thought there must have been some drastic escalation of tensions from North Korea.

"I was completely taken aback," the international politics expert from Macquarie University said.

"My first reaction was, 'Oh my gosh, has North Korea launched a strike or something?'"

Mr Yoon vaguely cited "anti-state forces" and "threats posed by North Korea" as reasons for the declaration.

But commentators say the declaration has nothing to do with aggressions from the north, and instead was about the domestic political impasse — including significant cuts to Mr Yoon's budget.

Danielle Chubb, an associate professor of international relations at Deakin University, said while relations between North and South Korea had deteriorated significantly over the past 12 months, there wasn't anything particularly new or noteworthy that would justify Mr Yoon's remarks, and he hadn't provided any evidence.

"It's just a thin pretext for a president who has been struggling … with legitimacy and struggling to overcome domestic political gridlock," she said.

"It's concerning because it hearkens back to the not-so-distant, but very dark authoritarian past, where any government opponents were tarred with this brush of being pro-North Korea."

She said even for observers watching South Korean politics closely, the move came as a "complete shock" because it was "so stunningly politically unwise".

"It's hard to see how this would have played out for him in a way that would be beneficial."

She said it was a relief there had been no loss of life during the chaos overnight.

Sung-Young Kim said anyone who visits Seoul frequently knows there are protests almost daily in front of the presidential Blue House.

"South Korea has a vibrant and a very hard-fought democracy … people have a long memory, I thought, surely this is going to be challenged."

Professor Chubb said there had been a fairly weak response from the US and Australia, rather than robust condemnation.

"Australia's focus and the US focus is always on South Korea as an important geopolitical strategic ally, and there's an unwillingness, I think, to really delve into some of this domestic political quagmire," she said.

Dr Jay Song also called on the Australian government to condemn Mr Yoon's actions. 

"South Korea's hard-won democracy is very fragile, but it is still a democracy," she said. 

"It's not just South Korea. I think it's a very dangerous political trend globally.

"This very sort of rogue, out-of-control leader can bring this chaos and mistrust and misinformation, and that can really erupt violent acts and conflict amongst people."