Police fears about a planned heist on a popular diamond exhibition has resulted in its closure.
The Millennium Star was among diamonds on display
The Natural History Museum's Diamonds show - billed as the world's largest collection - has attracted 70,000 people since it opened in July.
The museum said police advice changed suddenly on Tuesday so it closed it the following day, three months early.
The collection included the 203 carat De Beers Millennium Star, said to be the most valuable in the world.
It was the target of a foiled heist at the Millennium Dome in 2000.
Dr Michael Dixon, director of the Natural History Museum, said of closing the collection three months early: "Police indicated a heightened criminal risk to the exhibition. The museum's priority is the safety and security of our visitors and staff.
"Based on police advice, the only responsible course of action in this situation was to close the exhibition."
The exhibition was advertised as the world's largest-ever gathering of diamonds, bringing together "many of the most impressive single stones in the world".
Thousands of diamonds were on display, collectively worth millions of pounds, although the museum said it is impossible to put an estimated value on them as so many are classed as "priceless".
Other gems included the world's largest pink flawless diamond the Steinmetz Pink and the 407.48 carats Incomparable - the third largest cut diamond in existence.
Scotland Yard said detectives had been liaising with museum managers throughout the exhibition.
A spokeswoman added: "We have received information that leads us to believe that criminals were planning to target the exhibition.
"For the safety of staff, visitors and the exhibition specimens, we have advised the management to close the exhibition with immediate effect."