He called for "cast-iron guarantees" to secure AI in a speech ahead of the start of his second term in office as the United Nations High Commissioner for Human Rights.
Turk also demanded accountability over deaths in US immigration custody and condemned Russia's reported use of autonomous drones.
The wide-ranging address was his first to the 47-member council since he won the four-year term in July in the face of opposition from Moscow and Washington.
"I share the concerns of industry insiders that advanced AI could pose an existential risk to humanity," Turk said in Geneva.
"I am calling here, today, for an all-out effort to put cast-iron guarantees in place around the safety and security of AI, before it is too late."
Turk did not elaborate on the nature of the risks but a spokeswoman for his office said failures involving powerful AI systems could disrupt critical infrastructure and democratic institutions.
She referred to the "dangerous agent-training behaviours" in July's so-called Hugging Face incident - in which a swarm of OpenAI agents hacked an open-source platform - saying it suggested frontier AI capabilities are advancing faster than the safeguards.
Turk warned that just a handful of men held "almost unlimited power over AI" without naming any. Top AI companies include Meta, Anthropic, OpenAI and Google.
"At a minimum, we need countries hosting AI, and those involved in its supply chains, to come together around agreed red lines," he said.
The council is meeting until October 7 to discuss the war in Iran, Sudan's civil conflict and a string of other crises.
The US administration disengaged from the council last year, accusing it of anti-Israeli bias.
Turk called for accountability for around 23 deaths he said had taken place in US immigration custody so far this year and added he was concerned about plans to equip agents with electric-shock gloves.
The Department of Homeland Security has previously said it was committed to ensuring a "safe, secure and humane" environment in detention. Its inspector general is examining deaths in custody since October 2021.
Turk condemned Russia for its intensified attacks on Ukraine, and Iran for its rising number of executions.
He also voiced "horror" at reports Russia had used fully autonomous drones in Ukraine, allegedly killing three people in August.
"I join calls for the urgent prohibition of weapons that can take lives without human involvement," he said, referring to talks in Geneva.
With more than 60 wars around the world involving at least one state - the highest number since World War II - Turk set out ideas for ways to promote peace, pledging greater scrutiny of the businesses and economic interests that are fuelling conflicts.
"We will not shy away from exposing the shadow players and calling for accountability," he said.
