Tunnelling work between Jama Masjid and Delhi Gate metro station for Phase III project started on Tuesday.
A 96-metre-long completely assembled underground Tunnel Boring Machine (TBM) began the work.
It is the longest TBM ever used in Delhi Metro project and weighs approximately 500 tonnes.
"Its is the longest ever TBM and is the first ever to be inserted together. It will construct a 1,065 meter long tunnel (710 rings) and emerge at Delhi Gate on the up line," a DMRC official said.