The United Nations Security Council will hold its second secret ballot early tomorrow morning in its selection process for a new Secretary General to replace Ban Ki Moon.

Former Prime Minister Helen Clark finished sixth out of the 12 candidates in the first ballot on July 21.

She is aiming to improve on those results: eight "encourage" votes, five "discourage" and two "no opinion".

Only two women were in the top six, Clark and Bulgarian Irina Bokova, who was placed third.


But Bokova, the head of the UN's cultural organisation Unesco, is widely expected to face a veto from the United States if she is short-listed.

Clark has also headed a UN organisation, the UN Development Programme, for the past seven years.

Two other women have held highly placed roles in the UN: Susanna Malcorra was Ban's chief of staff until becoming Foreign Minister in Argentina last year; and Christiana Figueres headed the UN Framework Convention on Climate Change.

Four of the top five candidates in the first ballot were from Eastern Europe, the favoured region for those who believe the position should be rotated geographically.

The vote will be held about 2am Saturday (NZ time) and the results are expected to be known publicly two or three hours after that.

The ballots are secret in terms of how countries have voted for which candidates.