Police are treating the fire that destroyed flats next to the old Pavilion theatre as a suspected arson.
The large-scale fire started in the four-storey build next door to the Pavilion at the junction of High Street and Fountain Street at about 3.30am on Saturday.
Det Con Fred Winster, of Leeds District CID, said: “The cause of the fire is currently undetermined but it is being investigated as a suspected arson.
“The building was completely destroyed by what was a very significant fire.
“I would like to hear from anyone who saw anyone acting suspiciously in the area in the time leading up to the fire or who has any information that could assist the investigation.”
Watch Commander Lee Stone, of Morley Fire Station, said the entire building was engulfed when crews reached the scene in the early hours of Saturday morning.
He said: “When we got there it was through the roof.”
“Because of the proximity to the road and neighbouring buildings, our priority was to stop it spreading, and we were successful in doing that.”
Road closures were in place, with access between the South Queen Street junction with Fountain Street, Commercial Street and Middleton Road all closed.
The landmark Pavilion was built in 1911 and has been used as a theatre, cinema and bingo hall.
In 1990 it was converted into the After Dark nightclub and later became Puccino’s Restaurant.
The development next to it was so extensively damaged it will now be demolished, Leeds Outer South Neighbourhood Policing Team said.
A building to the back of the development was also damaged, but firefighters were able to stop the spread of the blaze further. Firefighters from Morley, Hunslet, Leeds, Cleckheaton, Dewsbury and aerial appliances from Leeds and Bradford stations were used.
Anyone with information is asked to contact DC 6344 Winster at Elland Road on 0113 385 9397 or via 101 or call the independent crime-fighting charity Crimestoppers on 0800 555 111.