Most of Queens erupted in panic and confusion—and a neon shade of blue—on Thursday night after a transformer explosion at a ConEd power plant shook buildings and projected what looked like a portal to another dimension into the city’s skyline.

As Twitter became flooded with messages from worried residents asking if the unnatural lights in the sky could mean the end of the world, or perhaps an alien invasion, other Queens residents reported hearing the sound of sirens and a loud, buzzing sound.

Astoria resident Ziad Elnokrashy told the New York Daily News he thought the city had suffered a “terrorist attack.” “Everything was flooded with smoke,” he was quoted as saying. “It looked like blue fire. It was so big it was like the whole sky turned blue… I thought it was the end of the world.”

As residents reportedly flooded into the streets to see what was happening, some were so scared they prepared to flee. “Once we saw people running, we decided to get out,” Peter Dipietrantonio, a resident who lives near the power plant, told The New York Times, adding that his girlfriend had frantically packed a bag and was “ready to go.”

Authorities were quick to reassure residents that the lights did not portend the end of the world, but rather an apparent transformer explosion at the ConEd power plant in Astoria.

“Confirming incident in #Astoria was result of transformer explosion. No injuries, no fire, no evidence of extraterrestrial activity,” the New York City Police Department tweeted.

An NYPD source told The Daily Beast a preliminary investigation had determined there were at least two explosions and at least one transformer had exploded at the Astoria East & North Queens Con Ed power plant. Only one employee was on the scene at the time of the explosion, the source added, and he was not harmed.

Deputy Inspector Osvaldo Nunez, the commanding officer of the NYPD’s 114th Precinct, told The New York Times the blinding blue light had caught even him off guard at the precinct about a half mile away from the plant.

“You felt it in your chest, the explosions, and the night sky turned an electric blue,” he was quoted as saying.

The NYPD later deemed the incident a “non-suspicious equipment malfunction,” and both Mayor Bill de Blasio and ConEd reassured residents that the situation was under control after what ConEd described as a “brief electrical fire.”

Con Ed spokesman Philip O’Brien told the Daily News there was “no explosion,” only a fire. The blue glow that nearly sent residents fleeing, he said, was caused by “electrical waves or currents.”

The incident briefly shut down LaGuardia Airport and left travelers frightened in the dark after the power went out inside the terminals, but authorities said air traffic control was not affected. After a 45-minute ground stop ordered by the FAA, the airport was back up and running just before 10:30 p.m., though some flights were reportedly canceled.

Rikers Island was also reportedly without power for about 25 minutes after the incident.

ConEd has said an investigation is underway into the cause of the fires but reassured residents that “ all power lines serving the area are in service and the system is stable.”