John Key resignation: World leaders respond

John Key and Malcolm Turnbull in better times (Twitter / file)
John Key and Malcolm Turnbull in better times (Twitter / file)

New Zealanders haven't been the only ones affected when Prime Minister John Key announced on Monday that he was resigning.

Australian Prime Minister Malcolm Turnbull says when he heard the news he texted Mr Key saying: "Say it ain't so, bro".

"He will be a great loss to New Zealand and a great loss to the world," Mr Turnbull says, calling Mr Key "one of the most outstanding national leaders in the world today".

"He has done an extraordinary job for New Zealand - he is somebody who all of us, right around the world, leaders in countries large and small, draw inspiration from."

On the world stage, Mr Key has been heard with levels of respect and attention "way out of proportion to the size of New Zealand", Mr Turnbull says.

Australian opposition leader Bill Shorten tweeted Mr Key had been a "good friend to Australia" and wished him and his family well.

Former Australian Prime Minister Tony Abbott, who was in power between September 2013 and September 2015 before being ousted, sayings Mr Key had a "fine innings".