Works to install a massive steel security fence across the lawns of Canberra's Parliament House won't be completed until June 2018.

On Tuesday, tourists and visitors watched as contractors used a large crane to install 2.6m prefabricated panels across the sloping lawns, which form part of the building's roof.

The fence is part of more than $126 million in security upgrades and fortification works planned for Parliament House.

Veteran press gallery journalist Michelle Grattan led criticism of construction, describing the fence as "appalling" on social media.