A loud explosion heard across much of Nevada and California has rattled homes and prompted a flood of calls to law enforcement agencies on both sides of the Sierra Nevada, some reporting fireball sightings.
The sound and the light show were likely caused by a meteor that entered Earth's atmosphere, astronomers said.
"It made the shades in my room shake hard enough to slam into the window a couple times," said Nicole Carlsen of the Reno area. "I kept looking for earthquake information, but (there was) nothing. I even checked the front of my house to make sure no one ran into the garage. I wish I had seen the meteor."
Erin Girard-Hudson of Arnold, California, told The Union Democrat of Sonora, that the loud boom that occurred around 8am Sunday (3am today, NZ time) made her two-year-old daughter, Elsie, cry.
"It knocked me off my feet and was shaking the house," she said. "It sounded like it was next door."
No damages or injuries were immediately reported. There were no reports of earthquakes at the time.
Some people reported seeing a brilliant light streak across the sky at the same time. Sightings occurred over roughly a 940-kilometre line across the two states, including Reno, Elko and North Las Vegas in Nevada, and the San Francisco, Sacramento and Bakersfield areas in California.
Astronomers said they believe the mysterious light was a fireball, which is a very bright meteor. It will take time to determine the path of the fireball and where it broke up, they added.
"From the reports, I have no doubt it was a fireball," said Robert Lunsford of the Geneseo, New York-based American Meteor Society. "It happens all the time, but most are in daytime and are missed. This one was extraordinarily bright in the daylight."
Lunsford said it's "pretty rare" for fireballs to produce a loud explosion. For that to happen, he explained, the meteor must have survived intact until breaking up about 8km above Earth. Most fireballs are visible at 80km above Earth.
"If you hear a sonic boom or loud explosion, that's a good indication that some fragments may have reached the ground," Lunsford told The Associated Press. "We'll have to get some people to work on it to pinpoint where it broke up and see if anything can be found on the ground."
Lunsford said more than 20 people in the two states had filed reports with his group by midmorning about seeing the fireball.
"I have been looking at the sky for 30 years, and I have never witnessed something so amazing and puzzling. It is an event that makes you glad to be alive," said Matthew Neal of San Francisco. "The main body was bright green and the head was bright red and white."
Greg Giroux of June Lake, California, located along the eastern Sierra just west of Yosemite National Park, also was impressed.
"This was by far the brightest fireball/shooting star I've ever seen, especially since it was in full sunlight," he said. "After the flash, it broke up into pieces, then I lost sight of it as it went behind a mountain."
In Nevada, the light show was seen as far east as Elko, about 480km east of Reno, and as far south as the Las Vegas area.
Marcia Standifer of Spring Creek, near Elko, and her husband were out drinking coffee when they saw the fireball at the same time.
"It was a very bright ball of white light, then dimmer to the horizon," she said. "We thought this was very unusual due to the bright daylight and how vivid the object was."
Tracey Cordaro of North Las Vegas said the sighting "took my breath away."
"It was amazing," she said. "It looked as if it was disintegrating rapidly, but was still quite large when it disappeared from my view ... (It was) bright green, visible in the bright sunlight."
Dan Ruby, associate director of the Fleischmann Planetarium at the University of Nevada, Reno, said it's unlikely the fireball had anything to do with the current peak of the Lyrid meteor shower.
"People are putting two and two together and saying it has something to do with the meteor shower," he said. "But the fireball was probably coincidental and unrelated to the peak of the meteor shower."
Though the fireball was seen over such a wide area, Ruby said it was likely just "a little bigger than a washing machine."