French firefighters work to tackle a fire on the roof of the luxury Ritz Paris hotel at the Place Vendome, central Paris, January 19, 2016. REUTERS/Jacky Naegelen

PARIS (Reuters) - Flames ripped through the top floor of the luxury Ritz Paris hotel on Tuesday, as around 60 firefighters battled to put out a fire which threatened the work of a 3-1/2 year restoration program just weeks ahead of a planned re-opening.

Some 150 workers were evacuated from the site in the chic Place Vendome square in central Paris at around 0500 GMT (12.00 a.m. ET), where about 15 fire trucks were on the scene, Paris fire service spokesman Captain Yvon Bot said on French television.

The cause of the fire, which struck on the seventh floor of the building and spread through the attic to the roof, was so far unknown, the official said.

By mid-morning, the fire had been brought under control, he told Reuters.

“There is no longer any risk of it spreading, but the operation will still take a very long time,” he said. The firemen had great difficulty accessing the part of the building affected, he said.

The Ritz had no comment as the incident was ongoing. The hotel’s website still indicated on Tuesday it was accepting reservations again from March 2016.

The former home of fashion designer Coco Chanel and author Marcel Proust, and a favorite drinking hole of American writer Ernest Hemingway, the hotel was last renovated over a decade beginning in 1979 after its purchase by tycoon Mohamed Al-Fayed.

The latest work to restore the Ritz, which opened in 1898 and was the first Paris hotel to boast electricity on all floors and bathrooms that were inside rooms, began in August 2012 and is being overseen by interior architect Thierry W. Despont.

It includes the building of a “discreet tunnel” that will enable the rich and famous to come and go in privacy. It was at the Ritz that Diana, Princess of Wales, spent her last night in 1997 before the car crash that killed her.