Sir John Key is playing down his Australian award.

The former Prime Minister will on Tuesday receive the country's most prestigious title, and become an honorary Companion in the Order of Australia.

Previous international recipients include Nelson Mandela, Mother Teresa and oceans explorer Jacques Cousteau, as well as other former political leaders from other countries.

Sir John told Newstalk ZB's Larry Williams he's touting it as a symbol of the Trans-Tasman relationship.

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"I just see it not as a reflection on me personally, but a sense of how strong the relationship is between New Zealand and Australia."

Sir John said he doesn't think it puts him on the same level as Mandela or Mother Teresa.

"Clearly there's been a reduction in quality since those fine people, but it's lovely for them to put me on the list and looking forward to it."

Only four other New Zealanders have been made an honorary Companion - one of them being former PM Sir Geoffrey Palmer.

Key will be appointed an honorary Companion in the Order of Australia in Canberra for his "eminent service to Australia-New Zealand relations".

A Companion is the highest ranking grade in the Order and 35 Australians every year can be appointed. Honorary appointments have been made to international figures with a close relationship with Australia.

Key said he was "completely shocked" but delighted when told of the honour.

"It reflects the closeness of the relationship as much as the individual. I always considered Australia to be our closest and dearest friend and so I tried hard to build a strong relationship with the Australian Prime Ministers that were there in my time."

Key said Turnbull would attend the ceremony at Government House as well as his guests - Key's wife Bronagh, his former Chief of Staff Wayne Eagleson, Foreign Minister Gerry Brownlee and Murray McCully, who was Foreign Minister throughout Key's time as PM until May this year.

Turnbull was also hosting drinks for them in Sydney on Monday night.

He and Key are close friends. Turnbull listed Key as his role model when he became Prime Minister of Australia and on an official visit to Australia, in 2016, the Keys stayed at Turnbull's Piper Pt home - a sleepover tagged as "Pyjama Diplomacy" by Australian media.

Australian Prime Minister Malcolm Turnbull is welcomed by former New Zealand Prime Minister John Key at Government House. Photo / Getty Images
Australian Prime Minister Malcolm Turnbull is welcomed by former New Zealand Prime Minister John Key at Government House. Photo / Getty Images

Key said the honour did not mean he would stop badgering Turnbull about the rights of New Zealanders in Australia, even though it was not his job any more.

"I'll still do it. I will take the opportunity to reiterate those points."

Australia's Governor General, Peter Cosgrove, will invest Key at the ceremony.

The citation for Key said it was for "eminent service to Australia-New Zealand relations" and said in his time as PM between 2008 and 2016, Key had raised the transtasman relationship to "new heights of co-operation and mutual confidence".

It pointed to measures such as trade liberalisation, Pacific relations and the work with Australia's troops in Afghanistan and Iraq.

Turnbull said it was the highest Australian honour.

"My instant, dismayed, reaction on his retirement last year was 'Say it ain't so Bro'. He has been a great friend of Australia and has represented his nation, and our shared values, magnificently.

"Lucy and I look forward to seeing more of John and Bronagh this side of the ditch and perhaps John and I can venture out for another paddle before too long."

He added: "John was an outstanding leader of his country, and he is respected around the world for his influence in our region and beyond.

"As Prime Minister ... he was also deeply committed to advancing the Australia-New Zealand bilateral relationship and pursuing our common interests in the region and internationally.

"Australia and New Zealand share a unique and close partnership, underpinned by shared history and values."