India, July 4 -- PJM, the largest power grid operator in the United States, said on Friday that it is facing serious pressure on the electricity system. The grid operator said it is working under a federal emergency alert to reduce electricity demand across its service area.

PJM said several problems are happening at the same time. Many electricity generators are currently out of service, reducing the amount of power available. High-voltage transmission lines are heavily overloaded, making it difficult to move electricity where it is needed, according to the report by Reuters. A long spell of extremely hot weather has led millions of people to run air conditioners, pushing electricity demand much higher than normal.

PJM has told utility...