Stunned residents of Orange County, California, watched in horror as normal programmes were interrupted by the terrifying alert.
An emergency message flashed up on screens across the area before a booming voice rang out from the TV, which some described as like Adolf Hitler.
It told them: “Realise this, extremely violent times will come.”
The voice added that the end of the world would take place on September 23.
After the chilling warning, social media was abuzz with debate about what had caused the prophecy.
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It coincided with widely-publicised claims by theorist David Meade that the apocalypse would begin on the same date.
Resident Stacy Laflamme told the Orange County Register: “It almost sounded like Hitler talking.
“It sounded like a radio broadcast coming through the television.”
And Erin Mireles said: “I was definitely startled because the volume increased exponentially.
“I wasn’t alarmed in the sense of thinking something was wrong, because I assumed it was some sort of hack.”
The problem has since been blamed on radio stations crying out emergency tests which were accidentally picked up by cable TV.
Cox Communications, whose broadcasts carried the message, apologised to customers and said the test was shut down once engineers became aware of it.
A spokesman told the paper: “We don’t want to alarm anyone with any false emergency alerts.”
Mr Meade claimed this month that, according to analysis of biblical texts and astronomy, Planet X would arrive on September 23 and herald the end of days.
For years he has been proclaiming the rogue planet, also known as Nibiru, is approaching Earth and will bring doomsday with it.
Some conspiracy theorists say that Nibiru will first be visible on September 23 as it approaches, but it will not actually be until some time in October that Earth will be obliterated.