Elon Musk's 'North Korea Nuclear UFO' SpaceX launch stuns Californians

A contrail of the SpaceX rocket is seen across the sky from Tijuana, Mexico on December 22, 2017. SpaceX blasted off a re-used Falcon 9 rocket on December 22, 2017 carrying 10 satellites into orbit, its fourth launch toward a $3 billion upgrade to Virginia-based Iridium's mobile, voice and data network. AFP PHOTO / GUILLERMO ARIAS

The launch of SpaceX's Falcon 9 rocket provoked wonder as it streaked across the early evening sky but also caused confusion, leading the company's founder Elon Musk to joke that the people had really seen a North Korean UFO.

The L.A. Times reported that SpaceX's 18th launch of the year took place at 5:27 p.m. The rocket blasted off from Vandenberg Air Force Base carrying 10 satellites, which it successfully deployed in a low earth orbit for Iridium Communications.

Related: Elon Musk Shows Off 27-Engine, $90 Million Falcon Rocket That He Expects to Fail

Authorities had warned Friday that the launch would be seen across the greater Los Angeles area and southern California but the sight still took many by surprise. The Associated Press reported that calls came into TV stations from as far away as San Diego, 200 miles from the air force base, questioning what had caused the lights.

Drivers stopped their cars on the freeways to take pictures and videos of the event. Tourists at Warner Brothers L.A. studio reportedly thought the long glowing trail in the sky was something to do with the movies.

Nuclear alien UFO from North Korea pic.twitter.com/GUIHpKkkp5

— Elon Musk (@elonmusk) December 23, 2017

One Twitter user, Max Power, tweeted to Elon Musk thanking him for "the hilarious alien debate that ensued between my family once we saw your rocket in the sky tonight."

Musk was happy to indulge the speculation. "It was definitely aliens," he replied on Twitter. Later, the SpaceX founder posted a video of the launch, captioning it "Nuclear alien UFO from North Korea."

The L.A. Fire Department had already put out an advisory saying the "mysterious lights in sky" were the result of the Vanderberg launch but this did not stop the speculation among Californians.

SpaceX used the same rocket in June to carry earlier Iridium satellites into orbit. In that instance, the first stage of the rocket landed on an offshore platform in the Pacific ocean. This time, the rocket was left to fall into the sea.

The launch was SpaceX's last of the year. The company has been contracted to replace Iridium's satellite system with 75 updated satellites. The work is expected to be completed by the middle of 2018 following four more launches. The satellites also carry technology for tracking aircrafts and ships around the globe.