The spill means Liberals will vote on the leader of the party for the second time in 10 months.

Senior Liberal sources, who have forecast tonight's spill for some days, say it's time to clear the air over the leadership, particularly now the release of Peter Costello's memoirs spell out the former Treasurer has no interest in leading the party.

Bu the meeting, held at 6.30pm in Canberra, came as a shock to many Liberal MPs.

In a statement following the meeting, Brendan Nelson said he was declaring the leadership of the Federal Parliamentary Liberal Party vacant.

It said he would be a candidate.

Opposition treasury spokesman, Malcolm Turnbull, has also declared his hand, and is believed to have the numbers, despite what was described as an "impressive" speech by the embattled Mr Nelson at the meeting.

"If I am re-endorsed as leader, I will remain absolutely determined and committed to the future of our party and Australia," Mr Nelson said.

"But as we move forward, I am asking our Party to draw a line in the sand and mark a transition – from the difficult aftermath of an election defeat to the building and presentation of a credible, attractive and inspiring alternative government.

"In doing so, we will make a renewed commitment to unity and discipline, to focus less on internal preoccupations and more on the Rudd Government, policy and the important issues concerning everyday Australians.

"Millions of Australians are counting on us – to hold the Government to account and provide Australians with a credible, attractive and inspiring alternative.

"I am asking my colleagues to make a renewed commitment to do just that."

It is believed Mr Nelson isn't crunching the numbers for his own support or canvassing any votes, but if he wins has promised big changes to the Opposition front bench.

* The results of the leadership battle will be posted on FarmOnline as soon as they are announced.