The family of Alek Sigley said they had no confirmation that the 29-year-old Pyongyang university student had been detained.
"Alek has not been in digital contact with friends and family since Tuesday morning Australian time, which is unusual for him," a family statement said.
"Alek's family hope to re-establish contact with him soon," it added.
Attorney-General Christian Porter, who is based in Sigley's hometown of Perth, told Perth Radio 6PR: "This particular jurisdiction, most Australians' common sense would tell them, makes this a matter of the utmost seriousness."
The Department of Foreign Affairs and Trade said it was providing consular assistance to the family.
"The department is urgently seeking clarification. Owing to our privacy obligations, we will not provide further comment," a department statement said.
Australia does not have an embassy in North Korea. Finance Minister Mathias Cormann, who is also based in Perth, said Australia's embassy in South Korea "has reached out to relevant officials in North Korea."
"There is obviously some complications in providing consular assistance into North Korea," Cormann told reporters in Japan. "We work through the Swedish government in North Korea and all of these steps are underway."
North Korea has been accused in the past of detaining Westerners for slight infractions and using foreign detainees as political pawns to gain concessions. As the country pursued diplomacy with the United States last year, it released three American detainees in what the nation's propaganda described as a gesture of goodwill.
Australia advises people to reconsider their need to travel to North Korea due to how its laws apply to foreigners and says foreign visitors have been subject to arbitrary arrests and long-term detentions.
The last Australian detained in North Korea was Christian missionary John Short, who was deported in 2014 after a 13-day interrogation.
Sigley said on social media that he was studying Korean literature at Kim Il Sung University and ran guided tours through a travel company he founded, Tongil Tours.
He told Australian Broadcasting Corp. two years ago that he wanted to break down negative stereotypes about the country.
"If we thought it was unsafe, we would stop doing these tours," Sigley said. "We wouldn't be able to bear the moral and legal responsibility of bringing people to North Korea if it was dangerous."
Official media in North Korea haven't mentioned the reported arrest.
Sigley's family described him as an Asian scholar and traveler who had visited, studied and lived in several countries.
He speaks Korean and Mandarin fluently as well as some Japanese, the family said.
He has traveled to North Korea several times since 2014, the statement said.
Sigley posted on social media pictures of his marriage to his Japanese wife Yuka in Pyongyang in May 2018. His family said his wife lives in Japan.
South Korean television station Channel A cited an unidentified source in reporting the arrest but the source told the network it wasn't immediately clear why Sigley had been detained.
In March this year, Sigley wrote for Guardian Australia about living in North Korea, saying that as a long-term foreign resident on a student visa he had "nearly unprecedented access to Pyongyang."
"I'm free to wander around the city, without anyone accompanying me," he wrote. "Interaction with locals can be limited at times, but I can shop and dine almost anywhere I want."
Australian National University in Canberra confirmed Sigley had graduated there last year with a bachelor of Asian studies.
"On behalf of the ANU community, I extend my concern and thoughts for his wellbeing, as well as to his family, his friends and colleagues," Vice-Chancellor Keith Nugent said in a statement. "We hope for a speedy and positive resolution to his reported situation."
In 2014, North Korea said it deported Short after he apologized for anti-state religious acts and requested forgiveness. He said later that recounting Biblical scriptures helped him endure the "long and grueling investigation."
Short said he "openly and honestly" admitted his crime as worded in the indictment: that he distributed Bible tracts with the purpose of making North Koreans become Christians.
Associated Press journalist Kim Tong-hyung in Seoul, South Korea, contributed to this report.
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