Around 20 firefighters are tackling a blaze close to the National Archives. London Fire Brigade said two disused water towers which were in the process of being decommissioned caught fire in Kew, south west London, at about 12.30pm.
Both towers are now "100% alight", a fire service spokeswoman said. A Scotland Yard spokesman said: "No-one is trapped or injured."
Police, who were called at 12.37pm, are providing assistance at the scene, he added.
More top news
A survey showing the number of 14-17 years olds who have tried the products has raised questions about their appeal to young people.
Top UK Advertising boss calls politicians to stop meddling in business and concentrate on creating wealth rather than spending cash
A touching note from a passenger thanking a pilot for getting her home safely in the wake of the Germanwings tragedy has gone viral.