He said there was more the UN, particularly the Security Council, could do to acknowledge and support regional leadership in the Pacific and elsewhere on peace and security matters. He said it was difficult to overstate the level of frustration "of the people I represent" with the complete inability of the UN Security Council to act in relation to Syria.
He questioned what it took for the Security Council to act when 25,000 had died, thousands were injured and many more thousands were displaced already.
"In the absence of leadership from the Security Council, I suggest that this [General] Assembly will need to find ways to play a more activist role."
Mr McCully's speech comes as New Zealand seeks a non-permanent seat on the Security Council for the 2015-16 term.
In New York he had almost 30 bilateral meetings with counterparts from other countries and many more informal discussions about the bid.
Turkey and Spain are also competing for the seat.
"We're up against two very large and powerful opponents so it's going to be difficult for us."
- additional reporting: APNZ