The 78th session of the UN General Assembly was declared open on by new General Assembly President Dennis Francis.

UN Secretary-General Antonio Guterres, in his opening remarks read on his behalf by his deputy, Amina Mohammed, warned of a world of deep challenge and division that is testing the United Nations, Xinhua news agency reported.

"Despite profound global challenges, this is not a moment for pessimism. This is a moment for action," he said on Tuesday.

"Action for peace and human rights; action to rescue the Sustainable Development Goals and tackle the existential threat of climate change; action to create productive jobs and expand economic opportunity, especially for women and young people; action to ensure that rapid evolutions in technology like artificial intelligence are a help, and not a harm, to humanity; action to build a world of hope and promise for all that leaves no-one behind."

"More than any room on earth, the General Assembly represents our common humanity and our shared commitment for peace, sustainable development and human rights. Let's forge the solutions that all people expect and make progress toward a better, and a more peaceful and prosperous future, and a healthier planet," said Guterres.

In his opening remarks, Francis said the new session of the General Assembly began "amid a daunting global agenda, beset by a series of cascading challenges".

He called on member states to push for and nurture peace by empowering those most vulnerable; to deliver shared prosperity by unlocking the resources required for transformational results; to accelerate progress by capitalising on the enablers of youth, innovation and technology; and to drive sustainability.

"This session, I will commit to engaging regional and other groups to collectively collaborate to bring to life a renewed atmosphere of global cooperation and shared commitments. My ambition is for the General Assembly to address the array of challenges it faces in the most effective and inclusive way possible," Francis added.

He called on member states to adopt a true spirit of multilateralism for problem-solving "so that we can better protect, if not guarantee, the security and dignity of humankind".

Francis, a diplomat from Trinidad and Tobago, was sworn in at the closing of the 77th session of the General Assembly on Tuesday morning.