Reaching out to the world's most isolated country can be extremely difficult, so Australian diplomats usually rely on a monthly fax or letter to communicate with North Korea.

The Department of Foreign Affairs and Trade has given an insight into its occasional interactions with Kim Jong-un's regime, during a Senate estimates hearing.

"The way the North Koreans communicate is typically a little unusual because we're not engaged with them as a close partner," DFAT Secretary Frances Adamson explained to the committee.

Although Australia and North Korea have a very hostile relationship Ms Adamson said there were "occasionally reasons to have contact".

"There are communications of various kinds, often it has to be said by fax machine, and occasionally by post, so it's not as if there's long periods of radio silence," the DFAT Secretary added.

The head of DFAT's North Asia division Graham Fletcher says Australia recently registered its anger at North Korea's nuclear test directly with the Kim regime.

"We seek to communicate with North Korea probably every month or two about one thing or another," Mr Fletcher said.

"Following their nuclear test on September 3 we sent a number of notes to them through New York, Beijing and Jakarta to protest at what they had just done and we sought permission to visit from our embassy in Seoul, which was not granted."

Earlier this month the North Koreans used their embassy in Jakarta to send a letter to Australia urging it to distance itself from the United States.

Australia does not have an embassy in Pyongyang and North Korea closed its embassy in Canberra several years ago.