The Metropolitan Police have announced that they received reports of a suspicious package in Duncannon Street.
They have evacuated Trafalgar Sq and offices nearby. They have also closed off Charing Cross underground tube station.
Specialist officers have been called in to investigate.
The entire square has been cleared and a cordone set up around the historic square.
Charing Cross station has been closed as a precaution and office workers are being told to stay inside.
This story is developing.