The confidence vote at the full-day caucus meeting was held at an old Church at Corbans Estate in Henderson.
On his way into the caucus, David Cunliffe said it was a secret ballot so he would not discuss how he would vote. In January he had said he would endorse Mr Shearer. Mr Shearer outflanked Mr Cunliffe in an effective challenge at the party conference last year.
Many other MPs going in also refused to say how they would vote, saying it was a secret ballot.
They included Cunliffe allies Nanaia Mahuta, Louisa Wall, and Charles Chauvel. However, Moana Mackey, another who is regarded as a supporter of Mr Cunliffe, said she would endorse Mr Shearer.
Other MPs also openly said they would vote for Mr Shearer, including Phil Goff, Chris Hipkins and David Clark, as well as Shane Jones, who said he hoped the venue of an old church would provide some "divine inspiration".
After this year, the new rules will require the confidence vote to be held soon after each election, rather than in the year preceding an election.