New Delhi, April 9 -- One person was dead and two were missing after a parking garage under construction in Philadelphia collapsed on Wednesday, officials said.

A roof segment fell and triggered a "progressive collapse of connected sections across all seven levels," Mayor Cherelle Parker told reporters Wednesday.

"Let me be very clear about something at this moment: We are not, we will not give up on these individuals and we will not rest until everyone is accounted for from this tragedy," she said.

Crews rescued three people, including one who was critically injured and later died at the hospital, said Philadelphia Fire Commissioner Jeffrey Thompson. Two others were treated and released.

He said the building is unstable and so they n...