A second rural Nevada county prepared Thursday for a "Storm Area 51" event that began as an internet joke but has drawn millions of social media fans.

Organizers of two festivals are inviting people to gather in tiny towns near the once top-secret U.S. Air Force test area known in popular lore as a site for government studies of outer space aliens.

An emergency declaration for Nye County took effect a day after county disaster preparation and sheriff officials told county lawmakers they're unsure how many -- or where -- people might show up for events Sept. 20-22.

"The information we're receiving would suggest ... we could have overwhelming population surges in various parts of the county," emergency manager Scott Lewis said.

Nye County, west and north of Las Vegas, has about 44,000 residents and is nearly the size of Vermont and New Hampshire combined.

Jon Koenig, chairman of the Nye County Commission, predicted that cellular phone service would crash because towers aren't equipped for a heavy volume of calls.

"There will probably be no water ... or ice available, because everything's going to sell out," he said during a Wednesday public meeting. "There will be no gas left in the gas stations. No food. Nowhere to go potty.

"If you're coming, be prepared, because it's not going to be nice," he concluded.

Sheriff Capt. David Boruchowitz said his department was advising people not to come.

County board members in neighbouring Lincoln County, which is about the size of Massachusetts, drafted a similar emergency declaration last week. They cited concerns about traffic jams, crowded makeshift campsites and a lack of nearby medical services. Officials count just 184 hotel rooms in the entire county.

Lincoln County also gave conditional approval to two events in the desert towns of Hiko and Rachel, nearest Area 51. Despite an initial internet post suggesting people rush the gates, festival organizers say they do not want people to try to enter the military base.

Final county approvals could come Sept. 3.

The events in Lincoln County would be about a 100-mile (161-kilometre) drive from Amargosa Valley, the Nye County farming community first identified as the place where people would gather to rush the gates of Area 51.

Last week, the Nye County Commission denied a permit for an event there that organizers dubbed "Peacestock 51."

CORRECTION: The Associated Press reported erroneously that organizers of festivals in two Nevada desert towns hope people will try to make their way into the once top-secret U.S. Air Force test base. Festival organizers say they do not want people to try to enter the military base.