Emergency services receive numerous calls about a loud explosion heard from Roselands to Marrickville, but cannot identify the source of the noise.
Experts are baffled by reports of an explosion that was heard in southwest Sydney, with no source or indication of where it came from.
Authorities received numerous reports from residents that they heard an "explosion" on Saturday night, but found no evidence of an explosion.
The NSW Fire and Rescue Service and NSW police responded to the calls but said they found nothing, not even fire, to indicate an explosion.
The incident is shrouded in mystery, as the sound was heard in Marrickville, Roselands, Bardwell Park, Campsie and Belmore.
Residents reported that the windows were shaking and the sound sounded like an explosion, but without any visual signs.
Since there is no sign of an explosion or any damage, and there is no identifiable source, residents are left wondering if the sound was a harbinger of some kind of devastating cataclysm.
Police said they were not investigating the incident and that they had received numerous calls about the apparent explosion, but did not know the source.
"Many calls were made to the emergency services, but the source of the noise could not be identified."
RFS also confirmed that it had not found the source of the sound, saying it could not have been electrical as there was no power outage or sound effects.
Sydney Airport also confirmed that there were no accidents on Saturday night, which rules out the possibility that it was a jet or an incident on the runway.
Brad Cooker, an astrophysicist at ANU, said there is nothing from space to explain this noise.
He explained that any celestial incident would have been heard far beyond southwest Sydney and noticed.
"If something like a meteorite falls from the sky, you can usually see a very bright blue or green flash."
"And when they're big enough to cause a sonic boom or be heard, they're big enough to burn quite brightly in the sky."
"It just seems odd that no one has seen anything."
The Defense Department did not respond to requests for comment on the incident.
"Yes, we are still trying to figure out what it was. It was like an explosion … We live in Bexley," Tina Tidroy wrote.
"Yes, I heard that from Bexley North. The sound was not like fireworks, it was like a real explosion," said Tamirez Alessandri.
"It's a mystery," wrote Rowena Phillips, "my parents heard 2 hits, and on the second hit the house shook." They live in Clemton Park near Kingsgrove North HS, so it must have been in the Kingsgrove area. Some here in Canterbury have heard it too."