Sense of global community 'may be disintegrating', Guterres says, resulting in diminished trust between nations.

The world is in trouble and faces "grave challenges", United Nations Secretary-General Antonio Guterres told global leaders Tuesday, striking a somber tone at the outset of the annual General Assembly in New York.

"People are hurting and angry. They see insecurity rising, inequality growing, conflict spreading and climate changing," Guterres said.

The sense of global community "may be disintegrating", Guterres said, resulting in diminished trust between nations.

"We are a world in pieces. We need to be a world at peace," the UN chief said.

Guterres highlighted the major issues facing the globe today, starting with what he called "the nuclear peril.

"The use of nuclear weapons should be unthinkable. Even the threat of their use can never be condoned," he said. "But today global anxieties about nuclear weapons are at the highest level since the end of the Cold War."

Guterres slammed North Korea's recent missile launches and its sixth and largest-ever nuclear test earlier this month, and he addressed the escalating rhetoric between Pyongyang and Washington.

"Fiery talk can lead to fatal misunderstandings," he said. "We must not sleepwalk our way into war."

Regarding the ongoing violence against the Rohingya Muslim minority in Myanmar, Guterres condemned what he termed a "vicious cycle of persecution, discrimination, radicalization and violent repression".

"We are all shocked by the dramatic escalation of sectarian tensions in Myanmar’s Rakhine state," he said.

"The authorities in Myanmar must end the military operations, allow unhindered humanitarian access and recognize the right of refugees to return in safety and dignity. They must also address the grievances of the Rohingya, whose status has been left unresolved for far too long," Guterres said.

With regard to climate change and controlling carbon gas emissions, Guterres said the science was "unassailable".

"We have had to update our language to describe what is happening: we now talk of mega-hurricanes, superstorms and rain bombs," Guterres said.

"I urge governments to implement the historic Paris Agreement with ever greater ambition," he said.

Guterres’ remarks come as one of the most important signatories, the United States, has repeatedly expressed its intention to leave the accord.

The UN chief also stressed the fight against terrorism, calling on world powers to address the root causes of radicalization. He also announced the establishment of the UN Office on Counter-Terrorism.

Guterres also touched on as the Israeli-Palestinian war, in which he said "today's stagnation" risked leading to "tomorrow's escalation".

The agenda for UN reform featured passingly in Guterres' address, in which he promised a "comprehensive reform effort".

The General Assembly will continue through the weekend, in which almost all UN member states take to the podium to speak of national and global issues.

The UN was founded in 1945 as a way to bring countries weary of two world wars around the same table in hopes of establishing lasting peace. Guterres took the helm as ninth secretary-general in January.