
For those San Franciscans who happened to be looking skywards on Saturday evening this was the ethereal and somewhat terrifying sight that greeted them shortly after 6pm.

With no prior warning and no immediate explanation - a nuclear-capable Trident missile was launched from a U.S. submarine off the coast of California and sent streaking in all its blue and white glory across the bay.

For a city famous for its lights, this one took the biscuit - and gave Twitter its very own nuclear meltdown with thousands speculating that it was a UFO.

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Awe-inspiring: These photographs capture the moment a nuclear-capable missile was fired off the coast of California and shot over San Francisco on Saturday night

Surprise: Photographer Abe Blair, 36, was taking pictures of the San Francisco skyline when a dazzling blue light streaked across the sky

He quickly grabbed his camera and managed to take these incredible images of the unarmed Trident II (D5) missile's launch (tail of streak, left) by a US Navy submarine

Photographer Abe Blair, 36, was taking pictures of the skyline when he spotted an 'unreal blue and white cloud just expanding bigger and bigger.'.

He said: 'The sunset was uneventful and the fog was a no show. My friend Justin and I decided to stick around and shoot some night images and play with some new techniques with our cameras.

'Then it happened. "What is that?!" we both yell as we are running to our cameras to recompose and try and capture this UFO as it headed right towards us.

'Just as we got our cameras reset it banked left out over the ocean. Over the next minute we watched it go and either leave our atmosphere or burn out.

Some time later a Navy spokesman confirmed that it was in fact an unarmed Trident II (D5) missile that was fired from the USS Kentucky, a ballistic missile submarine.

And the top secret military operations off the coast of Los Angeles has also forced aircraft at LAX, one of the country’s busiest airports, to take alternative routes for a week.

Mr had trekked up Slackers Hill in the hope of taking photos of fog and a sunset over the Golden Gate Bridge. This picture of San Francisco was taken moments before the unarmed Trident missile was fired

The Navy fired a nuclear-capable missile from a submarine off the coast of California, creating a mysterious streak (pictured) in the sky that sparked alarm on the West coast. Photographer Preston Newman (on Instagram at @Newman_Photos) was on a photo shoot at the time and captured the streak

Cmdr. Ryan Parry, of the Navy’s Third Fleet, said the Navy Strategic Systems Programs conducted the scheduled test flight at sea in the Pacific Test Range.

‘The tests were part of a scheduled, on-going system evaluation test,’ he told the San Diego Union-Tribune.

Cmdr. Perry said the launches are conducted on a frequent basis to ensure the continued reliability of the system. He added that information about such test launches is classified prior to the launch.

The test was conducted in the Pacific Test Range, a vast area northwest of Los Angeles where the Navy periodically test-fires Tomahawk and Standard cruise missiles from surface ships and submarines. Light from the test was seen as far away as Nevada and Arizona.

The entire operation is shrouded in mystery and even airport officials have said they remain in the dark over what is planned and why their usual airspace is off-limits.

Prior to the Navy’s announcement, thousands of residents, including celebrities, took to Twitter to share photos and video as well as their insight into what the light could be.

Grant Laughlin joined thousands of West Coast residents sharing pictures of the mysterious light that turned out to be a Trident missile test launch

Austin Whitlock shared an image (left) of the missile test seen from Burbank, California, while Patrick Folger, shared his view from Torrance (right)

Cmdr. Ryan Parry, of the Navy’s Third Fleet, said the Navy Strategic Systems Programs conducted the scheduled test flight at sea in the Pacific Test Range. Pictured: a Trident II (D5) missile underwater launch

Photographer Preston Newman shared a stunning image, with the caption: 'Couldn't believe what we saw during tonight's Downtown Los Angeles photo shoot! Can anyone explain this?'

And late on Saturday evening, the Orange County Sheriff’s Department tweeted: 'Light seen in OC sky was confirmed through JWA tower to be a Naval test fire off the coast. No further details.’

The mysterious light prompted reactions from celebrities as well, with Khloe Kardashian skeptical of those saying it was just a missile test.

'UFOs are real!!! Tripping out,' tweeted Khloe Kardashian. 'Kendall and I are spazzing out!!!#UFO,' she wrote just minutes later.

Khloe's supermodel sister Kendall Jenner was also in shock: 'Khloe and I are freaking out right now over this UFO situation,' she wrote.

Singer Josh Groban also couldn't help but look up at the glittering sky on Saturday night.

'California coast. DID. ANYONE. ELSE. JUST. SEE. THAT. #ufo,' Josh Groban tweeted.

Like Khloe, Groban wasn't convinced that an alien invasion was not underway.

'A test fire of what?! That is some unknown top secret stuff right there. Plus, X factor in all this, I was probed,' joked the singer.

Despite the confirmation that the light was a navy missile, a Darth Vader parody account jumped to take credit for the light.

'The UFO seen over LA tonight was just the Death Star getting into position,' he tweeted.

Conspiracy theory: "No further details" yeah ok..... Thanks that's because #WeAreNotAlone #AdmitIt,' Khloe tweeted after the Orange County Sherrif's Department shared an update on Twitter

Out of this world: 'UFOs are real!!! Tripping out,' tweeted Khloe Kardashian. 'Kendall and I are spazzing out!!!#UFO,' she wrote just minutes later

UFO: Josh Groban also saw the light in the sky and wondered if it could be the beginning of an alien invasion

They raised him up: Josh Groban says the light is in fact aliens and joked that they probed him