Tesla Motors CEO Elon Musk and famed theoretical physicist Stephen Hawking issued an open letter Sunday calling for artificial intelligence (AI) safety measures to be instituted.

Musk announced the open letter to his 1.44 million Twitter followers on Jan. 11.

"World's top artificial intelligence developers sign open letter calling for AI safety research: https://futureoflife.org/misc/open_letter," he tweeted.

The PayPal co-founder and electric-car mogul also expressed concern about autonomous systems in cars at Tuesday's Automotive News World Congress in Detroit.

"People should be concerned about safety with autonomous vehicles," Musk said, reports The Verge. "The standard for safety should be much higher for self-driving cars."

That was all Musk had to say at Congress, but he has previously compared rogue artificial intelligence to demons.

Musk and Hawking are not alone in their concern. Singularity theorist and science fiction author Verno Vinge and Lucasfilm's John Gaeta, the special effects expert behind the AI apocalypse film "The Matrix," digitally signed the AI safety document, as did MIT, Oxford, Stanford and Cambridge researchers. Google, Microsoft and Amazon executives added their names to the document, too.

The safety document, "Research Priorities for Robust and Beneficial Artificial Intelligence: an Open Letter," is a conservative approach to the topic with real fears of AI going rogue mentioned in the attached "research priorities document."

Mashable reports the most notable reference to artificial intelligence taking over is "Stanford's One-Hundred Year Study of Artificial Intelligence" that includes "Loss of Control of AI Systems." It explores the possibility that "we could one day lose control of AI systems via the rise of super intelligences that do not act in accordance with human wishes -- and that such powerful systems would threaten humanity."