Bloomberg said there was a push for a woman to take the role. However, it quoted John Langmore from the University of Melbourne saying Clark was "a stronger potential candidate than anyone from this region ever before" but it would be a tough race because of "strong sentiment" that Eastern Europe was next in line to have a Secretary General under the rotation of regions for the post.
China's state news agency Xinhua reported Clark had a reputation for maintaining New Zealand's independent foreign policy stance, "notably resisting calls to join the US-led invasion of Iraq in 2003."
Although the Eastern European issue could work against Clark, the candidate must be able to escape the veto of all five Permanent Members on the UN Security Council (the P5).
The UN Tribune said Clark was likely to be the favoured candidate for at least three of those five: France, the United Kingdom and the United States. It said the US had appreciated her decision to deploy troops to Afghanistan as former PM as well as her cost cutting at the UNDP.
However, the UN Tribune said she could run up against a brick wall when it came to getting Russia's support which was expected to favour an Eastern European candidate.
It also put up a more dubious possible objection to Clark's candidacy, saying because the Queen of England was New Zealand's head of state some UN states could claim it breached an understanding that the Secretary General should not come from one of the P5 countries.
In Australia, much of the focus was on what Clark's announcement might mean for Kevin Rudd who has reportedly been lobbying for support but has not yet announced a candidacy. Reuters and the Huffington Post said it would be a blow to Rudd's chances.
Although more people may nominate, Clark will go up against at least seven others - including three women. They are Unesco Director-General Irina Bokova of Bulgaria; former Moldova foreign minister Natalia Gherman and Croatia's former foreign minister, Vesna Pusic.
The other confirmed candidates are former Slovenia President Danilo Turk, former Prime Minister of Portugal Antonio Guterres, who was also a UN Commissioner for refugees and Montenegro Foreign Minister Igor Luksic.
Clark will have more than 40,000 staff under her and earn a tax-free base salary of about US$230,000 ($338,000) as well as free accommodation in New York if she is successful in her campaign to be the next Secretary-General of the UN.
However, the job has been described as the most difficult job in the world by the man who first held the role -Trygve Lie.
The Secretary-General oversees 41,000 staff worldwide who work for the UN Secretariat, of which about 6500 are based in New York and 21,000 are in field operations. Other UN organisations have a further 35,000 staff. The UNDP led by Clark has 7500 staff and Clark is on a base salary of about US$190,000 but her total remuneration has been estimated at US$450,000. She has previously said a "significant portion" of that goes toward paying for her New York apartment.
Based in New York, the UN website says the Secretary-General is "equal parts diplomat and advocate, civil servant and CEO". It describes the day-to-day work of a Secretary-General as ranging from attending the sessions of the various UN bodies to consulting with world leaders and extensive international travel to stay in touch with the UN member states.
Key attributes include integrity and impartiality and one of the most important roles is to use the "good offices" of the position, both publicly and in private, to help prevent international disputes arising or escalating. Although the UN Charter describes it as a "chief administrative officer" it also includes critical political and diplomatic elements. The Secretary-General has the power to raise with the Security Council any issues he or she believes threaten peace and security.
Commentators have observed that those who have held the role have adapted it to suit the problems faced in the world at a given time - the Council on Foreign Relations noted Kofi Annan was considered an "activist" and "world moderator" and his work earned him a Nobel Peace Price while current Secretary-General Ban Ki-moon was more of an administrator by nature and had focused on climate change and poverty.
In 1945, the qualities considered desirable included the leadership qualities to ensure the efficiency of the UN Secretariat, the skills to lead a team of people from different countries and build 'team spirit' and the moral authority to ensure the UN's independent role, as well as the ability to act as a moderator and informal adviser to governments.
Ban Ki-moon is the seventh Secretary-General to hold the role. It is appointed for a five-year term and a second term is often awarded. By tradition it is usually given to those from smaller- or medium-sized countries and nationals from the five permanent members of the Security Council - China, France, Russia, the United Kingdom and the United States - are not eligible. It has rotated through the various regions of the UN.
Other leaders react
Former Prime Ministers are among those starting to rally behind Helen Clark as she launches her campaign to be the next Secretary-General of the United Nations.
When announcing the Government's nomination of Ms Clark for the role, Mr Key said he expected former Prime Ministers and other prominent ex-politicians, such as Dame Jenny Shipley and Don McKinnon, to take on roles as informal envoys to help push for her election.
Former Prime Minister Jim Bolger, who also helped on the campaign to get on the Security Council, said the Government made the right move in nominating Clark.
He said she had the skills and experience for the role and was well known in New York. "But perhaps the strongest point - and this came through in the campaign for the Security Council which I was heavily involved in - is that New Zealand has a strong brand as a country that can address issues pragmatically, not get locked into one or other side. We don't claim as [former Australian Prime Minister] John Howard did that he was 'deputy sheriff' for America." He said the five permanent members on the Security Council (China, France, Russia, the United Kingdom and United States were critical in deciding who got the role and that could help Clark: "we have as good a relationship with all five without being locked into any as probably anyone."
Former Labour Prime Minister Sir Geoffrey Palmer said he would do what he could to help Ms Clark's cause with his international contacts.
"I'm very happy to be called on and very happy to help. I think it would be great for New Zealand if Helen were able to prevail in this matter." He said it would be a difficult field and could depend on whether Eastern Europe were able to get behind one candidate, but New Zealand should do what it could to back Clark. "There's a lot of people in this race, but it's going to be a woman I think."
He said he hoped that would be Clark.
"She's an extremely able person and she's had a lot of experience." He said he had seen that first hand in 2010 when he was in New York chairing the UN's Panel of Inquiry into the Gaza flotilla incident. "I think she'll be an admirable candidate."
Dame Jenny Shipley has not yet commented and a former Labour Prime Minister Mike Moore said he had no comment - Mr Moore returned to New Zealand from the United States in December after ill health forced him to give up his role as Ambassador to the USA.
The support of former politicians and Prime Minister John Key was echoed by current political leaders across the board.
Labour leader Andrew Little said he was proud of Clark, describing her as a "trail blazer."
"Renowned for her steely determination and formidable capabilities, she would make an excellent Secretary-General. I have immense trust in her judgement and values and I know she will have the whole of New Zealand cheering her on."
NZ First leader Winston Peters said he was pleased the National Government had followed the tradition of supporting erstwhile political opponents into international posts - as had happened with Mike Moore as director general of the WTO and Don McKinnon as Commonwealth Secretary General. ""We wish her nomination every success."
Green Party co-leader Metiria Turei said the Greens also supported Clark's bid: "It is time for a woman to lead the United Nations. Helen Clark has the experience and integrity to do the job."
