Mr Robertson said he sent his form in this morning and was confident he still had a significant core of support in caucus despite the entry of Andrew Little yesterday.
Labour's rules require candidates to be nominated by two fellow MPs.
Mr Robertson's choice of two of Labour's blokes and a Maori and a Pacific Islander as his nominees appears to be a message to those questioning whether his sexuality will put off morally conservative voters, such as religious Pacific communities.
His rival David Cunliffe had visited a Pacific Island church in South Auckland with MP Su'a William Sio recently and invited television to film him arriving.
Nominations for the leadership close next Tuesday and many are also expecting David Parker to announce he will run, although as of yesterday he said he had not changed his position.
After that, the candidates will embark on a three week road trip to win over the votes of party members and union delegates. The caucus vote is worth 40 per cent of the leadership vote under Labour's rules which also give the members 40 per cent and affiliated unions 20 per cent of the vote. Mr Robertson refused to say how much support he believed he had in caucus or name other MPs who are backing him.
When announcing his bid yesterday Mr Little also refused to name MPs he believed were backing him. He said today he expected to get his formal nomination in next Monday. David Cunliffe is expected to be nominated by Louisa Wall and possibly Nanaia Mahuta or Sue Moroney.
