Cinema staff evacuated a 100-strong audience after smelling smoke - only to find the blaze was at the neighbouring fire station.
Youngsters and their parents were halfway through a matinee showing of FairyTale - A True Story when the smoke wafted through the Duke of Yorks cinema, Brighton.
Concerned staff could not tell where the smoke was coming from so they stopped the film and asked customers to leave the auditorium.
Managers made sure everyone made their way safely outside while other staff called firefighters from Preston Circus fire station, just yards from the cinema.
But the fire crews from Green Watch who went into the roof emerged red-faced moments later after discovering the source of the smoke was a bonfire at their own fire station.
Sub Officer Steve Tomlin said: "We were burning off a load of rubbish from the station which we needed to get rid of.
"The bonfire was in the training yard but the smoke must have got through the gaps in the eaves of the cinema roof.
"Smoke filtered through the roof space and into the auditorium."
Paul Johnson, who was watching the film with his daughter, nine, and son, two, said: "We were sitting in the cinema and just after midday we started to smell smoke.
"The staff came in but they didn't know where the smell was coming from, or if there was a fire in the building."
Anthony Gates, duty manager at the Duke of Yorks, said the younger film fans had not seemed too bothered about missing the end of the film.
He said the children were very excited to see the firemen arrive and go into the building.
Mr Gates said parents would be given a free ticket for another of the Saturday morning Kids Club sessions.
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