The narrow margin of Mr Turnbull's victory suggests the party remains divided on its future direction, and paves the way for further division and instability.

It was after months of public speculation and internal debate about his performance that Dr Nelson last night declared his position open for a vote at this morning's Liberal Party meeting at Parliament House in Canberra.

Dr Nelson had hoped to ambush Mr Turnbull and his supporters.

While Mr Turnbull was on holidays in Italy - he only returned to the country on Sunday night - they had been leaking to the media suggestions that a challenge from Mr Turnbull would not happen until next month.

So sudden and unexpected was the announcement from Dr Nelson that even his key supporters did not know the move was coming.

However, it is believed that if Dr Nelson had not called the leadership spill, there were others in the party preparing to do so last night in order to bring the festering issue to a head.

Supporters of Dr Nelson had argued that he needed "clear air" in which to operate, having for months endured the distraction of speculation about the future of former Treasurer Peter Costello.

After Mr Costello last week announced he was not interested in the position, the way was left clear for Mr Turnbull to run against Dr Nelson.

The change in leadership comes just 10 months after Dr Nelson defeated Mr Turnbull for the position by just three votes in the wake of last year's Federal election.

Julie Bishop was unopposed to remain in the position of Deputy Leader.

* More details to come.