The organisers of Belsonic have issued a statement warning that their ID policy will be "strictly enforced" at this year's festival.
The event, at Ormeau Park, has an over-16s only policy and they say there will be no exceptions to that rule.
A spokesman added: "If you look under 21 you will be asked to prove your age. No ID, no entry, no refund.
"Accepted forms of photographic ID (no photocopies, photos of out-of-date IDs) include an official valid passport, photo driving licence, Government approved proof of age card pass, Electoral Card, Garda Card."
This year's Belsonic kicked off on Wednesday night with rock icon Slash and continues on Friday night (June 14) with Dimitri Vegas and Like Mike.
Stormzy, Ben Nicky, George Ezra, The Killers, Lewis Capaldi, Marshmello, Hozier and Tiesto are also bound for Belfast before the end of June.
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