SpaceX launched its Falcon 9 rocket on Friday night, creating a dazzling display in the sky above Southern California, and baffling some people who had no idea what was happening.

Watch some of the reactions from the ground:

"What did I just witness," one man asked:

What did I just witness?? pic.twitter.com/JsHfqTsxm0 — Danny United (@dannyunited) December 23, 2017

"It must be a comet."

"Are we about to die?"

Sharing one Twitter user's video, SpaceX CEO Elon Musk jokingly offered his own theory: "Nuclear alien UFO from North Korea."

Nuclear alien UFO from North Korea pic.twitter.com/GUIHpKkkp5 — Elon Musk (@elonmusk) December 23, 2017

The confusion prompted emergency calls in the city of Riverside, about 55 miles east of Los Angeles, where the Riverside Fire Department sent out fire engines after receiving calls of "something exploding in the sky," The Daily Breeze reported.

SpaceX launched this Falcon 9 mission from California's Vandenberg Air Force Base, carrying a collection of 10 satellites into low-Earth orbit. The payload is destined for a constellation of communications satellites owned by Iridium Communications. SpaceX conducted a similar launch for the same company in June.

Earlier on Friday, Musk offered photographic proof of a claim he made earlier this month — that he would launch his 2008 Tesla Roadster to Mars orbit in 2018. Musk, who also owns Tesla, shared a striking photo of the Roadster perched inside the carbon fiber fairing of a Falcon Heavy rocket.

"Test flights of new rockets usually contain mass simulators in the form of concrete or steel blocks. That seemed extremely boring," Musk wrote in his Instagram post.

Dave Mosher contributed to this report.