UFO enthusiasts drawn by alien-themed festivities have poured into rural Nevada near the Area 51 US military base, but fears of a mass raid on the remote site or a public safety crisis proved unfounded, with only five people arrested.
More than 3000 out-of-towners ventured on Thursday and Friday to the desert region around Area 51, a secretive US Air Force installation long rumoured to house government secrets about extraterrestrial life and spaceships.
The pilgrimage and two festivals welcoming the visitors were organised after a Facebook user jokingly exhorted readers to "storm" Area 51 on September 20 "to see them aliens".
Lincoln County Sheriff Kerry Lee said the region's guests were largely well behaved, with just a few exceptions. "I don't want to jinx myself, but so far it's gone pretty well," he said on Friday afternoon.
Three people were arrested on suspicion of trespassing onto the grounds of Area 51, Lee said. Another was arrested for indecent exposure after urinating near an entrance to the base, and a fifth for an alcohol-related incident, Lee said.
A steady stream of cars continued rolling into the county on Friday for events that were scheduled to run through the weekend.
The arrests were reported after a group of about 150 UFO fans and curiosity-seekers gathered outside the heavily guarded entrance to Area 51 around 3am on Friday, the date and time set by the social media invitation that went viral.
One man wore an orange space suit and some sported tin foil hats and alien masks. A sign among the gathering read "Free E.T. from the government."
One young woman ducked under a protective gate and was momentarily detained by authorities and released. Most showed no interest in crossing the barrier, according to law enforcement officials keeping watch over the crowd.
The Air Force had issued a stern warning to the public not to trespass on the installation, which it said is used to test aircraft and train personnel.
Area 51 had long been shrouded in mystery, stoking conspiracy theories that it housed the remnants of a flying saucer and the bodies of its alien crew from a supposed unidentified flying object crash in Roswell, New Mexico, in 1947.
The US government did not confirm the base existed until 2013, when it released CIA archives saying the site was used to test top-secret spy planes.