Whitehall and Trafalgar Square was closed while the Metropolitan Police "investigated an unattended item".
Westminster police posted a message on Thursday (June 15) morning at 7.20am letting people know of the security alert.
They wrote: "Whitehall & Trafalgar Sq is currently closed while we investigate an unattended item. Thank you for your patience."
Social media was awash with people sharing information on the closure, and people took to Twitter to warn others.
People were warned to "seek other routes" by TfL. Buses serving Trafalgar Square and Whitehall were diverted.
By 7.46am the roads had reopened.
The closure comes just a week after Trafalgar Square was evacuated and completely cordoned off by armed police following a suspect package alert.
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