Highlighting the "epic transformation" that the world is facing, Guterres addressed member states during the opening of the 79th UN General Assembly at New York headquarters.
"Our world is in a whirlwind. We are in an era of epic transformation -- facing challenges unlike any we have ever seen -- challenges that demand global solutions," said Guterres, adding that "geo-political divisions keep deepening."
Drawing attention to global warming, the UN chief said that "wars rage with no clue how they will end."
He underscored the threat of nuclear posturing and "new weapons cast a dark shadow."
"We are edging towards the unimaginable, a powder keg that risks engulfing the world," he said.
Guterres grounded his speech in two key realities: that the current global state of affairs is "unsustainable" and the challenges facing the world are "solvable."
"The level of impunity in the world is politically indefensible and morally intolerable," he stressed, lamenting that many governments feel entitled to disregard international laws, human rights conventions and UN resolutions.
"They can invade another country, lay waste to whole societies, or utterly disregard the welfare of their own people. And nothing will happen," he said, noting that the "impunity" can be seen in the Middle East, Europe, Africa and beyond.
On the Middle East, Guterres observed that "Gaza is a non-stop nightmare that threatens to take the entire region with it. Look no further than Lebanon."
Saying all states should be "alarmed by the escalation" between Lebanon and Israel, he said. "Lebanon is at the brink."
"The people of Lebanon, the people of Israel, and the people of the world cannot afford Lebanon to become another Gaza," he said.
He denounced the collective punishment of Palestinians, reiterating his demand for an immediate cease-fire and the start of a two-state solution.
"The speed and scale of the killing and destruction in Gaza are unlike anything in my years as secretary-general. More than 200 of our own staff have been killed, many with their families," he said.
Guterres contrasted the current global disorder with the more structured tensions of the Cold War era.
"For all its perils, the Cold War had rules. There were hotlines, red lines, and guardrails," he said, but now, the world is in a "purgatory of polarity" with many countries acting unaccountably in the absence of a stable world order.