The external planting facade was damaged by the fire, in addition to the roof and plant machinery on the roof.
The London Fire Brigade said: “The fire is believed to have been caused by the byproduct of arc welding landing on the felt lining of the planting facade.”
A spokesperson from the hotel said: “It is too early at the present stage to assess the full extent of the damage. A full investigation is underway and will take time to complete.”
The property recently completed the most extensive restoration in its 115-year history. As part of the renovation, the five-star hotel’s façade was revitalised, and designer Joyce Wang had transformed the lobby lounge and reception area.