Part of one of the arm-sized bolts fell onto the street and the area around the base of the building has been cordoned off to pedestrians.
Laing O’Rourke is main contractor on the tower dubbed the Cheesegrater.
O’Rourke and structural engineers Arup are now checking all 3,000 bolts on the building.
It is believed the bolts fell from the 15th and fifth floors of the tower.
Developer British Land issued a Stock Exchange statement which said: “Two steel bolts have recently broken on The Leadenhall Building.
“No one was injured in either incident and there is no risk to the structural integrity of the building.
“Public safety is our priority so we have taken a number of precautionary measures:
“A full investigation is being conducted by contractor Laing O’Rourke and structural engineers Arup.
“An examination is being undertaken of the remaining bolts. An area has been cordoned off around the base of the building while this process is ongoing.”
The bolts connect the nodes on the megaframe, but British Land said “the design of the structure allows for isolated events of this type and do not affect the structural integrity of the building.”