On the way into Parliament minutes after Mr Shearer's announcement today, Mr Cunliffe said he had "made no decisions'' about his own plans to run for the job and had learned of Mr Shearer's decision only at the caucus meeting called just before it was publicly announced. Mr Cunliffe lost to Mr Shearer in the runoff for the job after the 2011 election.
"I've made no decisions. I'll be consulting with party members, my LEC [electorate committee], supporters and I'll make up my mind over the next few days.''
Mr Cunliffe is regarded as having low levels of support in caucus, but the party's membership and union affiliates now have a vote which could be enough to override the caucus vote.
Mr Shearer's deputy leader Grant Robertson said he would not comment until after Question Time. He was not at Mr Shearer's side when Mr Shearer made the announcement - a sign Mr Robertson is considering running for the job.
Last year David Cunliffe was demoted by Mr Shearer after the party's annual conference, at which Mr Cunliffe repeatedly refused to express his support for Mr Shearer. Mr Cunliffe said today that he wished Mr Shearer well. ``He's made the very best contribution.''
Andrew Little, another MP regarded as having leadership aspirations, also refused to rule out trying for the role but said he had given "no thought'' to the matter.
"These are long, drawn out affairs sometimes.''
Mr Shearer was a man of "honour and integrity" in a difficult job, Mr Little said.
"It's really hard for us all that it should end in this way.''
Asked if it was damaging for the party to be facing another leadership change, he said: "Leadership contests are never a good thing for a party. That's just the reality of it.''
However, Labour's finance spokesman David Parker, who had withdrawn from the leadership race in 2011 to boost Mr Shearer's chances against Mr Cunliffe, said he would not put his name forward again.
Former leader Phil Goff also ruled out another tilt.
