Firefighters have tackled a blaze at the National Archives, home to some of the UK's most important historical documents.
London Fire Brigade said two disused water towers caught fire at the site in Kew, south west London, at about 12.30pm.
The main building, which was open to the public, was evacuated after the blaze broke out, a National Archives spokeswoman said.
Nobody was hurt and none of the documents were harmed, she added.
Clem Brohier, acting chief executive and keeper at the National Archives, said: "The most important thing is that no one was hurt and no documents were damaged in this incident.
"I have seen for myself today how quickly the London Fire Brigade got here and how staff from The National Archives swiftly put our incident plan into action and the public responded calmly and helpfully."
The spokeswoman said: "The fire affected two water towers next to the main building. None of the documents or any people were harmed."
Investigators are still trying to determine the cause of the fire, although there is "no indication" it was started deliberately, she added.
The National Archives are expected to reopen to the public on Tuesday.
More than 20 firefighters spent an hour tackling the blaze after both towers were "100% alight", a fire spokesman said.
He said: "The fire caused significant damage to the water towers and smoke could be seen from the surrounding area."
Four fire engines went to the scene from Kingston, Richmond, Wandsworth, and Hammersmith fire stations.
The National Archives is the Government's official archive of original documents and records, dating back more than 1,000 years.