The incident took place around 5.00 am near Lady Shri Ram College in Dhamrutpur near Lajpat Nagar.
Delhi Metro spokesperson Anuj Dayal said, seven persons were injured in the incident, while eyewitnesses pegged the figure at over 11. The injured have been rushed to the AIIMS.
He also said, "a structural collapse and we are investigating the matter. It appears there is a problem in design of the peer of the bridge. We were trying to rectify it."
Two other labourers are still trapped in the debris, he added. All those injured in the incident are labourers of the contractor, Gammon India.
The under-construction bridge fell on a water pipeline which led to some flooding in the area. An eyewitness said 20-25 labourers were working on the site.