Captain Bot said the alarm was raised at about 7am. Some 200 workers who were in the building have been evacuated. The blaze was unusually difficult to access and control, he added.
The area was blocked off at the height of the rush-hour, while firefighters on cranes sprayed the flames.
Princess Diana and Dodi Fayed were staying at the Paris Ritz on the night they died in August 1997.
The Princess dined with Mr Fayed in the hotel’s Imperial Suite before leaving in a car driven by the Ritz’s deputy head of security, Henri Paul.
Their Mercedes, pursued by a pack of paparazzi, crashed at high speed in the Pont d’Alma underpass, leaving only one survivor, bodyguard Trevor Rees-Jones.
The hotel opened in 1898, with proprietor César Ritz promising guests “all the refinement that a prince could desire in his own home.” It was the first hotel in Europe to provide en-suite bathrooms and telephones and electricity in every room.
The inspiration for Irving Berlin’s 1929 song Putting On The Ritz, it has appeared in numerous books and films including The Devil Wears Prada and From Russia with Love, as well as the Audrey Hepburn movie Funny Face.
Designer Coco Chanel lived in a suite that bears her name, and called it “ma maison”. During the Second World War it was the local headquarters of the Luftwaffe and Hermann Goering lived in the Imperial Suite.
Charlie Chaplain was also a guest and in 1944 Ernest Hemingway arrived in Paris on a tank and boasted about “liberating” the main bar.
He later wrote: “When I dream of afterlife in heaven, the action always takes place in the Paris Ritz.”
But in recent years the Ritz was felt to be living on past glories and in 2011 it failed to qualify for a new category of “palace” hotels in Paris, prompting the huge refurbishment.
