Building engineers examine 744 similar windows in Gherkin as plaza is sealed off to protect passers by.
There are questions marks over the safety of the Swiss Re façade today after a glass window fell 400ft to the ground.
The Plaza at the base of the tower was sealed off after the triangular window smashed and fell.
A Swiss Re spokesman said that the window was open at the time and 744 similar windows have now been secured in the close position.
The spokesman said that it has began an investigation into the incident and said that building engineers were inspecting similar windows.
A piece of wood has been used to cover the window space and scaffolding is in place around the entrance of the tower to protect visitors.