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.
Residents living close to a disused building gutted by fire in Cardiff have been relocated while investigations into the blaze continue.
Fire crews were called to Pearl Street, Splott, at around 12.40pm on Monday and spent much of the day extinguishing the flames.
Surrounding properties were evacuated and residents have been relocated or are being supported at a local authority rest centre while the building's safety is assessed. Agate Street, Pearl Street and Splott Road are all closed. Police say it's still too early to say what caused the fire.
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.