Police and fire services are still at the scene of the fire in a disused building in Pearl Street, in the Splott area of Cardiff.
A South Wales Police spokesperson said the fire was reported at around 12.40pm.
Road closures affecting Agate Street, Pearl Street and Splott Road are in place.
Firefighters say there's a risk that a fire-hit building in Cardiff could collapse.
Roads around the old Bingo hall in Pearl Street are still closed and an investigation continues.
Rain clipping the far north through the evening but elsewhere staying dry with some sunny spells.
Public Health Wales figures show 25 more cases of the virus have also been confirmed.
Photos taken on Saturday morning show Roald Dahl Plass strewn with empty beer bottles and discarded canisters of laughing gas.