UPDATED 2.45PM: Helen Clark is facing an uphill climb in her campaign to become UN Secretary General.

The straw poll overnight puts her in eighth place out of 10, one place lower than the previous two polls.

She was given six "encourage", seven "discourage" and two "no opinion" votes.

In the only positive sign, in the third poll she had six "encourage", eight "discourage" and one "no opinion".

Her office said this result is a pleasing improvement.

The established frontrunner, former Portuguese prime minister Antonio Guterres, came out on top again.

Prime Minister John Key said one less country discouraging her from going on was an encouraging change, and the net result was good.

"I've had a brief text conversation with her this morning about that, so obviously we're pleased. But look, the reality is, we're very much in those early stages. There's a lot of work to be done. There's some candidates in front of her that are still polling very, very well."

Key said the change in vote could have come from the US but it’s impossible to know for sure.

"What people say and how countries ultimately vote, as we know in these types of contests, are quite often different and difficult things to decipher."

Foreign Minister Murray McCully said the signals both he and Key had been given was that Security Council members wanted Clark to remain an option on the shortlist once the vetoes came into play.

He said in the past all Eastern European contenders had been vetoed out when it was Eastern Europe's turn.

"It is important to have people like Helen Clark available if we do get to that point."

While that might not happen this time he was certain some of the candidates above Clark would fall. 

"When you look through the list this time it is very easy to see many of those who fare better than Helen Clark through the straw polls are going to go the way of the veto. So if we look at a net list of candidates for the short list, I think she's in reasonable shape and is justified in making the decision to stay in the contest."

The straw polls are held in secrecy and while the overall results have been leaked there is no indication of the way individual Security Council members have voted.

That will become clear in October when the first ballot with coloured papers is held - including which candidates will be vetoed by permanent five members of the Security Council: China, France, Russia, the United Kingdom and United States.

Russia has been lobbying strongly for an eastern European candidate, while other nations, including the US, are believed to be pushing for the next UN secretary-general to be a woman.

In the first poll Clark came sixth and in the second and third polls she fell to seventh.

With the drop to eighth, she trails Guterres, Slovakia's Foreign Minister Miroslav Lajcak in second place, former Serbian foreign minister Vuk Jeremic in third, former Macedonian foreign minister Srgjan Kerim in fourth, UNESCO director-general Irina Bokova of Bulgaria fifth, former Slovenian president Danilo Turk sixth and Argentinian Foreign Minister Susana Malcorra in seventh.

Clark has said it's a tight pack and she intends carrying on with her campaign.

Voice of America's UN correspondent Margaret Besheer said Clark began as a strong candidate, but for some reason isn't succeeding in the polls.

"She's just not really resonated with the council members and she's been solidly in the middle of the pack and now she's just dropped down to the bottom."

A fifth Security Council vote will be held on September 26, with the plan to recommend a consensus candidate to the 193-member UN General Assembly in October.