UFO enthusiasts drawn by alien-themed festivities continued to pour into rural Nevada on Friday 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 three people arrested.

An attendee wears an alien mask at the gate of Area 51 as an influx of tourists responding to a call to 'storm' Area 51, a secretive U.S. military base believed by UFO enthusiasts to hold government secrets about extra-terrestrials, was expected in Rachel, Nevada. 

An estimated 2,300 out-of-towners ventured on Thursday and Friday to the desert region around Area 51, a secretive US Air Force installation long rumored to house government secrets about extraterrestrial life and spaceships.

The pilgrimage and two festivals welcoming the visitors were organized after a Facebook user jokingly exhorted readers to "storm" Area 51 on Sept. 20 "to see them aliens." The date chosen for the gathering was never explained.

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.

One person was arrested, and another briefly detained, on suspicion of trespassing onto the grounds of Area 51, while two other people were arrested for indecent exposure and an alcohol-related incident, Lee said.

A steady stream of cars continued rolling into the county, and Lee said he expected the turnout to double or triple as more visitors arrived for the weekend.

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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 3 a.m. 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."

"A bunch of random people in weird costumes standing outside of a government base, why would you want to miss that?" said a YouTube personality who goes by the name Atozy. "That's a once-in-a-lifetime experience."

One young woman ducked under a protective gate and was momentarily detained by authorities and released. Others stayed outside the perimeter, according to law enforcement officials keeping watch over the crowd.

"They're just here to see what's going on," said Sergeant Orlando Guerra of the Nevada Department of Public Safety Investigation Division. "They’re here to have fun."

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.

The documents, however, did not end suspicion about space aliens there.

Area 51 sits about 12 miles (19 km) from the tiny town of Rachel, a community of about 50 year-round residents north of Las Vegas that hosted a music festival to entertain those traveling to the region.

Some residents had urged the public to stay away for fear the town would be overwhelmed with unruly tourists.

As of early Friday, roughly 2,000 people had pitched camp in town, most of them outside the Little A'Le'Inn, an alien-themed motel and restaurant that is Rachel's only business. Another 250 attended a separate event 40 miles away in Hiko that featured musicians and ufologists.

Ed Callahan, 49, who drove from Victorville, California, to Rachel, described the atmosphere as "just chill."

"It's not this big, wild thing," said Callahan, who sported a cowboy hat covered in tin foil and silver tentacles. "When they said 40,000 people, I didn't want it to be that. If a few more people show up, it'd be alright."

Connie West, the Little A'Le'Inn co-owner who scrambled over three months to mobilize for an influx of alien fans, said she was gratified that chaos failed to ensue.

"I'm relieved the naysayers were proven wrong," she said.