Serial entrepreneur Elon Musk is not averse to burgeoning technology like space flight and driverless cars. But when it comes to artificial intelligence, he's frightened.

At the National Governors Association Summer Meeting in Rhode Island on Saturday, Musk called AI the "biggest risk we face as a civilization." He expressed his concern about machines and software taking control over humans, and called on the government to regulate AI before things escalate.

"I have exposure to the very cutting edge AI, and I think people should be really concerned about it," Musk said at the event. "I keep sounding the alarm bell, but until people see robots going down the street killing people, they don't know how to react because it seems so ethereal."

Musk wants the government to be proactive about AI regulation. He believes the current model is reactive, allowing the government to step in only after "a whole bunch of bad things happen." He called this setup inadequate because the technology represents "a fundamental risk to the existence of civilization."

This isn't the first time Musk has spoken out about the issue. The Tesla and SpaceX CEO said that his hope to colonize Mars is partially a backup plan in case AI takes over Earth, according to Vanity Fair. The first step in regulating such a new industry, Musk said, is "to learn as much as possible, to understand the nature of the issues."