The Bulletin of the Atomic Scientists (BAS) said it had acted because the world was becoming "more dangerous".
The clock, created by the journal in 1947, is a metaphor for how close mankind is to destroying the Earth.
It is now the closest to the apocalypse it has been since 1953.
That was the year when the US and the Soviet Union tested hydrogen bombs.
Last year, the clock was also moved forward by 30 seconds.
What was behind the decision?
Announcing the move in Washington DC on Thursday, the BAS said the decision "wasn't easy" and said it was not based on a single factor.
However, BAS President and CEO Rachel Bronson said that "in this year's discussions, nuclear issues took centre stage once again".
The team of scientists singled out a series of nuclear tests by North Korea. They dramatically escalated tensions on the Korean peninsula and led to a war of words between North Korea and the US.
The BAS also referred to a new US nuclear strategy that was expected to call for more funding to expand the role of the country's nuclear arsenal.
Rising tension between Russia and the West was also a contributing factor.
Chart showing adjustments to Doomsday Clock since 1947
The "weakening of institutions" around the world in dealing with major global threats - including climate change - was another major concern, the scientists said.
They also mentioned US President Donald Trump's "unpredictability", pointing to his often controversial tweets and statements.
Trump's year on Twitter: Who has he criticised and praised the most?
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