Fire ripped through a building in the Chinatown area at 2.15am, just yards from the ethnic quarter’s imperial arch.
A number of roads in the city centre were blocked by the fleet of fire engines sent to tackle the flames.
Due to falling debris, firefighters were initially forced to keep back from the multi-storey commercial building, which was left severely damaged.
Crews and dogs searched the building once the fire was under control, amid fears homeless people were sleeping inside.
The blaze was contained by around 6am. But Portland Street, Princess Street and Faulkner Street remained closed.
Speaking from the scene, fire service spokesman Paul Etches said: “It is very, very unsafe in there at the moment and very difficult for crews to get in and work in and around.
“We have still got pockets of fire and quite a large area of the building has suffered quite a serious partial collapse.
“The roof has burnt through and it is very, very difficult to search the second and third floors of the building.”
He said it was too early to determine the age or sex of the victims.
Asked to comment on rumours that the bodies were those of rough sleepers, he said: “We have heard the same but at this time there is nothing, no intelligence, we have found. It is too early to tell.”
Chief Inspector Gareth Parkin said: “These are tragic circumstances and we working to identify the people who were found in the building.
“A joint investigation with the fire service is in its early stages and we will be carrying out a number of enquiries to establish how this fire started.
“I would appeal to anyone with any information about this incident to please call us.”
Information can be passed on to police by calling 101 and quoting incident number 146 of 25 November 2016 or Crimestoppers anonymously on 0800 555 111.