The central arch of Waterloo Bridge has been shut to boats for urgent safety checks "due to material falling from the expansion joints," the Port of London Authority has announced.
A harbour service launch with a flashing blue light was stationed under the arch on Friday evening to alert boat crews to the closure.
On Saturday signs were installed to show that the arch is out of use.
The PLA says that "detailed examinations in order to determine necessary repairs are to take place in the week commencing 28 November".
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