"The situation is that Alek has not been in digital contact with friends and family since Tuesday morning, Australian time, which is unusual for him", they said in a statement.
Attorney-General Christian Porter told local radio that the effort to confirm the status of Sigley is "a matter of the utmost seriousness". They said they are urgently looking for clarification about his whereabouts.
Yet, Sigley's writing on the country were largely positive - he even held his wedding, to a Japanese wife, in North Korea - raising further questions over the reasons for his arrest.
It is the North Korean embassy - Pyongyang's closest diplomatic outpost to Australia - one of 50 the Democratic People's Republic of Korea maintains across the globe.
South Korea's National Intelligence Service, the country's main spy agency, said it can not confirm the report.
In a post in January this year, Sigley described a strong interest in East Asia and "socialism" and recounted his first visit to North Korea in 2012.
North Korea has been known to detain foreigners - including the shocking case of Otto Warmbier, a college student who was released in a vegetative state back to the US. As the country pursued diplomacy with the United States past year, it released three American detainees in what the nation's propaganda described as a gesture of goodwill.
Sigley, a postgraduate student of Korean literature at Kim Il Sung University, founded Tongil Tours in Australia in 2013, according to the company's website.
"If we thought it was unsafe, we would stop doing these tours", Sigley said.
"Alek was the people-to-people ambassador in North Korea".
Official media in North Korea haven't mentioned the reported arrest.
The family of Alek Sigley, 29, said that they remain in the dark whether he was arrested in the country where he lived and studied at the Pyongyang university.
His family said on Friday that they had no news about whether he has been detained.
Chad O'Carroll, CEO of NKNews publisher the Korea Risk Group, said in a statement Sigley was a knowledgeable observer of North Korea and that the publication was surprised by reports of his sudden detention.
There are no posts on Sigley's Twitter account after June 24.
Leonid Petrov, an Australian National University expert on North Korea and friend of Sigley, suspected that the missing Australian had been "deliberately cut off from means of communications" temporarily because Trump was in the region.
Mr Sigley, who has been a resident of Pyongyang since early 2018 and who is believed to be the only Australian living in the hermit kingdom, studies contemporary North Korean literature and has written regularly for Western media outlets about his day to day experiences. "Interaction with locals can be limited at times, but I can shop and dine nearly anywhere I want", he wrote in the Guardian.
Australian National University in Canberra confirmed Sigley had graduated there a year ago with a bachelor of Asian studies.
"Those offers of assistance have been genuine, but I must say our key focus at the moment is to ascertain precisely where Alek Sigley is and in what circumstances".