Candidates vying to become the next UN secretary-general fielded questions Tuesday on global crises -- from climate change to Middle East conflict -- during the first-ever hearings to chotose the world's top diplomat.

The United Nations opened the three days of public hearings in a packed chamber, breaking from the secrecy that has surrounded the choice of the UN chief throughout its 70-year history.

Three of the nine contenders made their pitch to the General Assembly's 193 nations, laying out their vision as the successor to Ban Ki-moon, who will hand over on January 1.

For decades, the choice of the UN chief has been firmly in the hands of the Security Council and its five permanent members -- Britain, France, China, Russia and the United States -- in a process largely kept behind closed doors.

But the General Assembly last year voted to shake up the process, asking candidates to send a formal application letter, present their resumes and appear at hearings.

The final decision to nominate a candidate still rests with the Security Council, but the new openness could put some pressure on big powers to pick a nominee with broader appeal.

"This is a potentially game-changing exercise," General Assembly president Mogens Lykketoft told reporters.

"If there is a critical mass of countries supporting one single candidate, I don't think we will see the Security Council coming up with quite a different name."

Montenegro's Foreign Minister Igor Luksic -- at 39, the youngest of the candidates -- was up first, switching from English to French in an address that touched on his Balkan roots and ways to improve the UN bureaucracy.

Bulgaria's Irina Bokova, who heads the UN cultural agency UNESCO, said the United Nations should do more to combat violence against women and stressed the importance of gender equality.

Seen as Moscow's preferred candidate, the 63-year-old ex-foreign minister is considered a strong contender in the race that could see the first woman chosen as secretary-general and the first eastern European.

Russia has said that the next UN chief should come from eastern Europe, the only region that has yet to be represented in the top post.

During the two-hour session, Bokova steered clear of controversy and sought to portray herself as a candidate of continuity ready to "serve" UN member-states.

On the Israeli-Palestinian peace process, Bokova said she would work to "build trust and confidence" between the parties but stressed that on many complex issues, she did not have "the magic bullet."

"You will see the new secretary-general serving you," Bokova said in her message to member-states.

Too many meetings

Former high commissioner for refugees Antonio Guterres spoke bluntly about the UN's shortcomings, calling for a more results-orientated work culture.

"Let's be clear: We have too many meetings, with too many people, discussing too many issues with too little decisions," said the former Portuguese prime minister.

Recalling his work as a young volunteer in the slums of Lisbon, the 66-year-old pledged to act as "a convener, a facilitator, a catalyst, an honest broker, a bridge-builder and an ambassador for peace."

The race to be UN secretary-general will pick up steam in July, when the Security Council begins the rounds of straw polls to measure support for the candidates.

Final polling is expected to take place in September, when the 15-member council will submit one nominee to the General Assembly, which is expected to endorse the choice.

Six more candidates will take part in hearings this week: Slovenia's former president Danilo Turk, the ex-foreign minister of Croatia Vesna Pusic and Natalia Gherman, the former foreign minister of Moldova.

The head of the UN Development Programme and New Zealand's former prime minister Helen Clark will speak on Thursday, as will Macedonia's former foreign minister Srgjan Kerim.

Serbia on Tuesday put forward former foreign minister Vuk Jeremic as a candidate and he will take part in hearings on Thursday.

More candidates are expected to come forward, including two women seen as potential frontrunners -- EU Commissioner Kristalina Georgieva of Bulgaria and Argentina's Foreign Minister Susana Malcorra.