Six fire crews were sent to tackle the blaze after the alarm was raised at around 1am.
Watch manager Keith Williams, from Buckley Hill fire station, Netherton, said: “There’s not a lot left of the restaurant. It’s in ruins – completely destroyed.
“There’s not a lot left of the first floor either.”
The nightclub next door was also left smoke-logged.
Up to 14 fire fighters fought their way into the burning building, following reports there were people inside.
But, after the search of the premises, no-one was found and police said no one was injured in the fire.
Fire crews raced back to the scene at around 9am after the flames reignited. The flames were dampened down quickly.
The Serenity Spa was attacked over the Easter weekend when a petrol bomb was thrown through a broken window.
The spa is now open again.
Witnesses should call Copy Lane CID on 0151 709 6010 or Crimestoppers anonymously on 0800 555111.
