Both the mishaps took place yesterday when portion of two structures at Vasai and Kopri areas in the district came down crashing, they said.
Nanita Pagi (16), who was injured in the wall collapse of an under construction building in Vasai, succumbed to her injuries this afternoon, police said.
Twenty-four other injured have been admitted to a hospital in Vasai.
In another incident, a wall of a building in Sidhivinayak Nagar in Kopri, collapsed leaving two persons injured, who have been hospitalised at Veer Savarkar facility at Mulund.