Liberal members have endorsed a motion championed by former prime minister Tony Abbott to allow plebiscites to select candidates for state and federal seats in NSW.

Sitting members would also be open to challenge under a motion passed at a special convention in Sydney on Sunday afternoon.

It was expected the vote would be close, but former MP Ross Cameron said the final tally was 748-476.

There was a hitch when the electronic voting system crashed for almost half an hour just before 3pm, which meant the votes of 1500 members had to be cast again.

A how-to-vote card issued by backers of the so-called Warringah motions, which were moved on Sunday afternoon, called on members to vote "yes" only to the two motions, and "no" to the dozens of others.

"Stop the factions, stop the stacking, take control of your party," the card read.

It is understood key proponent, retired major general Jim Molan, received loud applause in moving the motions.

It is understood Mr Molan successfully moved to cut short the debate and bring on a vote.

Voting is still to come on a series of other reform motions.

The voting system involves a website which can be accessed via smart phones, tablets and computers.

Some members were allowed to vote manually if they did not have electronic devices.

One NSW Liberals member, Kevin Brennan, tweeted before the debate: "If the one member one vote motion doesn`t get passed in the NSW Liberal party convention today then the election is lost+ the party finished."

A party insider told AAP it was likely several of the motions could get a majority of votes on the floor, and it would then be up to party officials to weave them together into what has been described as a "modernisation plan".

The plan would go to a NSW Liberals state council meeting later in the year for endorsement.

Prime Minister Malcolm Turnbull spoke in favour of plebiscites at the convention on Saturday as a way of giving more power to members and building the party's membership base.

He described plebiscites as a "fundamental element of party democracy".

However, there are differences of views over the checks and balances in the system, including a minimum period of membership of the party.

Mr Abbott told reporters on Saturday those who opposed his "one member one vote" motions were advocating "fake democracy".

It is expected some disgruntled conservative party members could quit the Liberals if the reforms don't go far enough.

The current preselection practice involves a combination of branch-elected local delegates and "central" electors from outside the seat.

AAP