The major fire which tore through a former school in Newhaven is being treated as suspicious.
Sussex Police said three local children, two girls and a boy, all aged 13, were arrested on suspicion of arson following the blaze at the Grays School site in Western Road.
They have been released under investigation while enquiries continue.
The fire, which started shortly before 11am yesterday (Monday, December 18), caused extensive damage to the derelict building but nobody was hurt.
East Sussex Fire and Rescue Service investigators are due to return to the scene today (Tuesday, December 19).
Crews from across East Sussex spent most of yesterday battling the flames and people living in the Western Road area were advised to close all windows.
At its height, eight appliances were at the scene together with extra water carriers and two aerial ladder platforms.