Donald Trump's presidency poses a great threat to the world, the scientists found
Scientists are expected to move the clock's hands to two minutes to midnight on Thursday, with 00.00 representing the end of humanity.
The countdown, established in 1947 by experts building the first atomic bomb in America, was created to demonstrate in the simplest way possible of how much danger the Earth is in from nuclear war.
The Bulletin of the Atomic Scientists currently has the clock pointed to 23.57 but as of tomorrow it will move to 23.58.
Tensions between the United States and Russia that remain at levels reminiscent of the Cold War
Bulletin of the Atomic Scientists
The move will mark the closest the world has ever been to global obliteration since 1953 when the United States boosted its nuclear capacity with the hydrogen bomb.
2015 was the last time the clock was moved, when it was shifted forward by two minutes to its current time.
The panel of Nobel Laureate scientists will announce the clock will go to 23.58 tomorrow
As well as nuclear obliteration, the Doomsday Clock also looks at other emerging threats such as advances in biotechnology and artificial intelligence, as well as climate change.
In December, the Bulletin hinted the Doomsday Clock was about to move closer to midnight.
The scientists released a statement which said: "Tensions between the United States and Russia that remain at levels reminiscent of the Cold War, the danger posed by climate change, and nuclear proliferation concerns – including the recent North Korean nuclear test – are the main factors influencing the decision about any adjustment that may be made to the Doomsday Clock."
And on Sunday, two days after Mr Trump's inauguration, the organisation posted a warning which said: "Terrorism involving nuclear or radiological materials remains one of the gravest threats to humanity and to global stability."
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The nuclear scientists also warned about any "accidental, unauthorised, or inadvertent nuclear exchange between the United States and Russia".
They added their concern was bolstered by the fact the two countries have 800 warheads are on high alert, ready to launch.
The nuclear threat from North Korea is very high the scientists have said
The Bulletin of the Atomic Scientists believe nuclear war is more imminent than in recent years
In an event to be streamed live at 3pm GMT on Thursday, the Bulletin will announce the new "time".
The clock remained unchanged last year and over the past six decades has been moved forwards and backwards, but tomorrow's alteration marks a terrifying move which is closer to the early days of hydrogen bomb testing and 1984, when US-Soviet relations were at "their iciest point in decades".
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Russia is estimated to have around 7,300 nuclear warheads. Of these, an estimated 1,790 are strategically deployed.
When the clock's hands were moved forward in 2015, the scientists said: "Three minutes to midnight is too close. Far too close.
"We, the members of the Science and Security Board of the Bulletin of the Atomic Scientists, want to be clear about our decision not to move the hands of the Doomsday Clock in 2016.
"That decision is not good news, but an expression of dismay that world leaders fail to focus their efforts and the world's attention on reducing the extreme danger posed by nuclear weapons and climate change.
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"When we call these dangers existential, that is exactly what we mean: They threaten the very existence of civilisation and therefore should be the first order of business for leaders who care about their constituents and their countries."
Tomorrow's statement is expected to be even more severe.
When the clock started in 1947 it was set to seven minutes to midnight and in 1991 – when the Cold War officially ended – it reached its safest point at 17 minutes to midnight after the Strategic Arms Reduction Treaty reduced the number of strategic nuclear weapons deployed by both the US and Russia.