Strange, spiraling light patterns in the night sky of New Zealand baffled and amazed stargazers on Sunday night.

Alasdair Burns, a stargazing guide on Stewart Island/Rakiura, received a text from a buddy at about 7.25 pm, telling him to go outdoors and look at the sky. "As soon as we actually went outside, it was very obvious what it was he was referring to,”  Burns recalled.

In the midst of the blackness, he noticed a massive blue spiral of light. “It looked like an enormous spiral galaxy, just hanging there in the sky, and slowly just drifting across,” Burns described, adding that it was “quite an eerie feeling.”

Burns took a couple of long-exposure photos of the lights, capturing the spiral with his phone. “We quickly banged on the doors of all our neighbors to get them out as well. And so there were about five of us, all out on our shared veranda looking up and just kind of, well, freaking out just a little bit.”

People posted images and inquiries about the phenomenon, which was visible from most of the South Island, on the country's stargazing and amateur astronomy social media groups. Theories abound, ranging from UFOs to alien rockets to commercial light shows.

“Premonition from our orbital black hole,” posted one stargazer.

Another commented that it was “aliens at it again."

The truth was probably more mundane, according to Prof Richard Easther, a physicist at Auckland University, who described the occurrence as "weird but easily explained."

He described such clouds as occurring sometimes when a rocket carried a satellite into orbit.

According to Easther, “When the propellant is ejected out the back, you have what’s essentially water and carbon dioxide – that briefly forms a cloud in space that’s illuminated by the sun,” adding that “the geometry of the satellite’s orbit and also the way that we’re sitting relative to the sun – that combination of things was just right to produce these completely wacky looking clouds that were visible from the South Island.”

Easther believes the rocket in issue was the SpaceX Globalstar mission, which was launched into low-Earth orbit off the coast of Florida on Sunday.

Burns suspected the spiral was generated by a rocket after reading about a similar phenomenon in 2009 when a Russian missile launch caused massive blue spirals above Norway. Even knowing the likely source, he said it was a startling sight. “None of us had ever seen anything like that before. It was spectacular.”