The Bulletin of the Atomic Scientists, which set up the clock at the start of the Cold War, shifted the clock to 89 seconds to midnight, a week after the inauguration of US President Donald Trump.

The clock was last moved to 90 seconds to midnight over nuclear-armed Russia's invasion of Ukraine in 2022. It was originally placed at seven minutes to midnight in 1947.

"At 89 seconds to midnight, the doomsday clock stands closer to catastrophe than at any moment in its history," said former Colombian president Juan Manuel Santos, chair of The Elders, a group of major former leaders, as he presented the findings by a board of experts.

"The clock speaks to the existential threats that confront us and the need for unity and bold leadership to turn back its hands," he told a news conference in Washington.

Just days into his second presidency, Trump has already shattered norms on international cooperation

Santos welcomed Trump's pledges for diplomacy with Russia and China, but condemned his withdrawal from the Paris climate accord and World Health Organization.

The experts warned of the worsening impact to the planet of climate change after another record-breaking year of high temperatures.

Santos also called for "urgent actions" to tackle disinformation "and the amplifications of conspiracy theories that have become so prevalent in our hyper-connected online world."

"This alarming rise in distrust is being fueled in large part by the malicious and reckless use of new technologies we do not yet fully understand," he said.