Emergency services were called to the Le Confidante brothel on Elizabeth Street, Surry Hills, about 4am on Monday and found the three-storey building alight.

The fire spread through the roof and into the adjoining terrace house, before 16 firefighters extinguished the flames, Fire and Rescue NSW Superintendent Phil Lindsay said.

"There was a fire at the same property a week ago," he said.

No-one was injured and there were no evacuations.

Earlier, police and firefighters were called to Eagle Boys on King Street, Newtown, where they found a fire burning in the foyer.

"There was forced entry to the building and a strong smell of petrol," Superintendent Lindsay said.

Police established a crime scene and are now investigating the fire, which caused an estimated $10,000 worth of damage.

Early on Monday morning, 35 firefighters battled a huge fire at Kleenheat depot, a gas cylinder re-filling factory, on Grand Avenue, Rosehill.

"When firefighters arrived there were large volumes of black smoke and there were a number of gas bottles exploding," Superintendent Lindsay said.

The fire was under control by about 7am and did not spread to adjoining factories.

A statement from Kleenheat said no gas cylinders exploded.

Police established a perimeter around the factory and warned drivers to be careful as smoke drifted over the area.

Investigators will look into the cause of the fire.

Initial information suggested the blaze started in a re-filling booth inside the single storey factory and was possibly accidental.