Among those, 45 will represented by their heads of state or heads of government who will be asked to pledge funds and make commitments for action during the May 23-24 summit.
Stephen O'Brien, the UN under-secretary general for humanitarian affairs, yesterday said he found the turnout "so far encouraging", even though it amounts to fewer than half of the UN's 193 member-states.
He declined to name the leaders attending or give details of the countries that have accepted the invitation, saying only that they represented a diverse group of nations.
World governments, international organisations and aid agencies are struggling to cope with the largest refugee crisis since World War II affecting 60 million people on the move.
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Globally, some 125 million people are in need of aid and, this year, the relief efforts will require a record USD 20.1 billion in funding - five times the amount a decade ago, according to UN estimates.
Every year, 218 million people are affected by disasters.
The three-day gathering will seek to chart a course with new strategies to address humanitarian crises and the rising cost of aid efforts, said O'Brien.
Part of the discussion will focus on striking a "grand bargain" between donor nations and UN agencies to help address the funding crises, O'Brien said.
The goal would be to "try to get a better predictable financial base to support humanitarian action in exchange for more effective delivery of those goods," said O'Brien.
The heads of leading international aid organisations and some private sector representatives will be among the 6,000 delegates at the summit, which has been in preparation for the past three years.