UPDATED: 8.38AM Those wanting to become UN Secretary-General have begun making their pitches to the General Assembly.

They've included one of the candidates seen as Helen Clark's biggest threats -- Bulgarian Irina Bokova.

Bokova's told delegates equal opportunities for men and women and the integration of migrants should be at the core of the United Nations' efforts during the next Secretary General's term of office.

Bokova argues no sustainable development is possible if men and women are not offered equal opportunities.

America University's Professor Michael Schroder told Mike Hosking Bokova is seen as the front runner and Russia wants a European candidate in the job.

He said because this is Eastern Europe's turn, it will be a hurdle for Helen Clark.

"This horse treading that goes on, it is possible that Helen Clark manages to become the nominee. It's still a long shot although maybe not as much of a long shot as it was a year ago or six months a go."

Voice of America's Margaret Besheer told Rachel Smalley the most impressive performer was Portugal's former Prime Minister António Guterres.

LISTEN ABOVE: Margaret Besheer talks to Rachel Smalley

"I think he really led on all fronts. He had charisma, he was competent, he knew the issues, he had real answers for the questions. Whereas I think some of the other candidates have been lacking all those areas."

Besheer said there's a degree of anticipation around Helen Clark's delivery tomorrow morning.

"She said herself, she knows how to build coalition. She's a proven leader and that's what the UN needs." 

Professor Schroder said the selection process has become more open.

He said now candidates are formally nominated and potentially meet the the entire membership at these general assembly interviews.

"I think it's important to be realistic here. At the end of the day, the formal process of the election itself will still take place largely behind closed doors, as far as I can tell, in security council deliberations."

Besheer said a wild card could still enter. 

Candidates have until June to put their hand up.