THE BRONX - A massive power outage in Co-op City overnight left more than 50,000 people in the dark and without air conditioning.

Officials say the community's main power plant failed at around midnight, and the backup generator didn't kick in, affecting more than 15,000 apartments. Four people were rushed to the hospital with chest pains and breathing problems because their oxygen machines stopped working.

Emergency workers responded immediately, and all power was restored by 6 a.m. with the use of electricity from Con Edison. They say an investigation is under way to figure out why both the plant and generator failed.

The Riverbay Corporation's plant, which is the city's first tri-generation power plant, was first turned on in 2008. The $65 million system is supposed to use less fuel, cutting greenhouse gas emissions and other pollutants by 40 percent.

New power plant in Co-op City helps residents go green