Antonio Guterres, who takes over from Ban Ki-moon on January 1, also said the UN needs to be more nimble and less bureaucratic.
He spoke after meeting with Chinese Foreign Minister Wang Yi in Beijing. China is one of the UN's largest financial backers, and Guterres said it could be an important peace broker in conflicts around the world.
Guterres told a news conference that he wants to make sure the different parts of the UN "work for the same purpose" without duplicating efforts. He said they also need to be subject to independent public evaluation.
The United Nations has been in the spotlight over allegations of child rape and other sexual abuses by its peacekeepers, particularly in Central African Republic and Congo.
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Guterres, a former prime minister of Portugal and head of the UN's refugee relief agency, said the world faces challenges from enduring conflicts, climate change, population growth and water scarcity that are "making more and more people suffer in different parts of the world."
Wang said the 193-member UN needs to be more efficient in its governance and better able to respond to emergencies.
China is the biggest contributor of UN peacekeepers among the five veto-wielding permanent members of the Security Council, having sent more than 30,000 on 29 separate missions.
President Xi Jinping said last year that China would also set up a permanent peacekeeping standby force of 8,000 troops to be deployed whenever necessary.
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