The United Nations Climate summit (COP15) is likely to reach a final deal as world leaders were beginning to arrive at Copenhagen.

We know what we must do. We know what the world expects. Our job here and now is to seal the deal, a deal in our common interest, UN Secretary-General Ban Ki-moon said Tuesday at a ceremony which marked the formal opening of the final high-level stage of the ongoing meeting.

He also said that three years of effort have come down to three days of action. Let us not falter in the home stretch. No one will get everything they want in this negotiation .

Mr. Ban warns the world leaders to face a defining moment in history. He says the next three days as the most complex and ambitious ever to be undertaken by the world community.

Meanwhile a key Australian Kyoto negotiator says he is confident that a final deal will be reached by the end of the week.

This is actually unprecedented - when under a UN process that's actually designed to lead to a political agreement, to have global leaders stake their reputations on that outcome, former Australian government minister Robert Hill said.

I think it shows me that they have a vested interested in a good outcome, that's what they need to go home and say they achieved, so I think it can make a significant difference in this instance, he said.

Regarding to the protests, walkouts and accusations of fraud, Mr Hill said I do know there is a lot of theatre in this town today. I suspect there will be a lot of theatre tomorrow as well. But in the end it will be what's on the table that will count.

Danish Minister Connie Hedegaard who hosts the climate summit also warns that “In these very hours we are balancing between success and failure. Success is within reach. But I must also warn you: We can fail.”