National Concert Day -- which, as made-up holidays go, is a pretty worthy one -- brought together a stunningly eclectic collection of artists to celebrate at Irving Plaza on Tuesday.

"We feel y'all's love, y'all's loyalty," said Florida Georgia Line's singer/guitarist Brian Kelley, following a short set of the country duo's hits. "You guys have changed our lives. Seriously."

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Swae Lee -- one half of the brotherly duo Rae Sremmurd -- said his first concert left him with the feeling that "something amazing was just out of his reach." However, now that the hip-hop hitmakers behind "No Flex Zone" are headliners themselves, playing The Emporium in Patchogue on June 4, they say they are out to make as intense an impression on their fans.

Swae Lee said that being picked as openers for Nicki Minaj's tour, which stops at Barclays Center July 26, was "like we're accepting an award or something."

Live Nation New York President Jason Miller said his company created the day as a long-overdue national kickoff to the summer concert season. "There's no better time than right now to experience live music," he said. "It's still one thing that you can never replicate . . . We can only share being together in that moment live."

To encourage people to get out to see more live music, Live Nation is offering those who buy a pair of tickets to a show at Nikon at Jones Beach Theater by May 9, a $30 voucher good toward another pair of Jones Beach tickets.