Alek Sigley, the Australian student who is uncontactable in North Korea / Courtesy of the Sigley family via AP

The Facebook page of an Australian man missing in North Korea reappeared then disappeared again on Saturday hours before Prime Minister Scott Morrison said Australia is still trying to find out what has happened to him.

Alek Sigley, one of only a handful of Western students in the secretive country, has been missing for several days.

His family had taken down his social media accounts to prevent unnecessary speculation online.

Sigley's Facebook page reappeared overnight, but it is not known who reinstated it, or why.

It had disappeared again on Saturday by 2 p.m. Sydney time (0400 GMT) and remained down on Sunday morning.

Sigley's Twitter account has remained online and members of the public have posted messages of support there.

The missing man's last posts on his Twitter and Facebook profiles are from Monday, June 24, and his family has not heard from him since Tuesday.

Speaking from the G20 Summit in Osaka, Japan, Prime Minister Morrison said he had spoken to Sigley's family and said Australia was still trying to find out what happened to him.

"I will just be measured in what I say because that is all about using the best opportunities we have right now to, to inform ourselves about where Alek is and what his safety is and where he is being held, in what conditions," he told reporters on Saturday evening.

Morrison said numerous world leaders had offered help to find Sigley and bring him home.

When asked if U.S. President Donald Trump's visit to the Korean demilitarized zone (DMZ) presented an opportunity for the Americans to make representations, Mr Morrison said he would not allow the issue to be taken up with other agendas.

"We're going to work with everybody to secure Alek's safety and the best way we can do that is doing it quietly, effectively, working with our partners," he said.

"This is, not allowing this to be taken up into other agendas, it's not about that, it's simply for me, about Alek's safety. Sorry."

The 29-year-old Australian moved to North Korea to study for a master's degree in Korean literature at Kim Il-sung University in Pyongyang, and also ran a small tour company specialising in educational trips to North Korea.

Sigley has been an unusually active social media user for someone living in North Korea, updating his social media accounts with photos and blog posts about benign subjects such as food and fashion.

The treatment of foreign citizens by the secretive North has long been a contentious issue.

American student Otto Warmbier died in 2017 after being detained in North Korea for stealing a propaganda poster from his hotel room. (Reuters)