Malcolm Turnbull (left) will be succeeded by Scott Morrison. Photo: AFP

Mr Turnbull had been under pressure from poor polling and what he described as an "insurgency" by conservative MPs.

Mr Morrison, the treasurer, won an internal ballot 45-40 over former Home Affairs Minister Peter Dutton - who had been Mr Turnbull's most vocal threat.

Mr Turnbull is the fourth Australian PM in a decade to be ousted internally.

"It has been such a privilege to be the leader of this great nation. I love Australia. I love Australians," he said on Friday.

Mr Morrison entered the race after Mr Turnbull lost key backers. After a majority of MPs called for a leadership "spill", Mr Turnbull agreed to step down.

With a mixture of bemusement, anger and sheer frustration: many have described this week as one of the most chaotic in Australian political history.

In his final press briefing, Mr Turnbull called the week "madness" and thanked his colleagues for choosing Mr Morrison over Mr Dutton.

"We have so much going for us in this country. We have to be proud of it and cherish it," he said.

Not a single leader in recent times has succeeded in serving a full term as prime minister, partly because elections come around so often - every three years.

So in recent years, prime ministers unpopular in the polls - or with their colleagues - have been swiftly sacrificed from within.

Under the Australian system, as in the UK, the prime minister is not directly elected by voters but is the leader of the party or coalition that can command a majority in parliament.