An urgent investigation has been launched after a piece of falling masonry on the parliamentary estate was blamed for smashing a car's windscreen.
Tory MP Will Quince said it was evidence of why Parliament needs "urgent repair".
The incident happened at around lunchtime on Thursday (October 19) outside the Grade I-listed Norman Shaw North building, used as offices by MPs.
A parliamentary spokesman said: "The main entrance to Norman Shaw North has been closed for health and safety reasons until further notice.
"The incident is being investigated by parliamentary authorities as a matter of urgency."
Colchester MP Mr Quince tweeted a picture of the smashed windscreen of the Toyota Prius and said: "This stone fell off the top of a building. Imagine if this had hit someone. Unthinkable." He later deleted it for "security reasons".
Fellow Conservative Mims Davies said the incident was "absolutely shocking" and occurred near her office.
"Very glad nobody was very seriously injured or, heaven forbid, even worse," she added.
The building was originally used as the headquarters of the Metropolitan Police Commissioner, when it was known as New Scotland Yard.
It was designed by architect Richard Norman Shaw and built between 1886 and 1890.
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