People cool off at a fountain in New York, the United States, on July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

People cool off at a fountain in New York, the United States, on July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

People cool off at a fountain in New York City, the United States, July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

People cool off at a fountain in New York City, the United States, July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

People cool off at a fountain in New York City, the United States, July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through. (Xinhua/Li Muzi)

People cool off at a fountain in New York City, the United States, July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

People cool off at a fountain in New York City, the United States, July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

People cool off at a fountain in New York City, the United States, July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

A child cools off at a fountain in Washington D.C., the United States, on July 20, 2019. The highest temperature reached 36 degrees Celsius in Washington D.C. on Saturday as a result of a prolonged heat wave. (Photos: Xinhua)

A boy cools off at a fountain in Washington D.C., the United States, on July 20, 2019. The highest temperature reached 36 degrees Celsius in Washington D.C. on Saturday as a result of a prolonged heat wave.

Children cool off at a fountain in Washington D.C., the United States, on July 20, 2019. The highest temperature reached 36 degrees Celsius in Washington D.C. on Saturday as a result of a prolonged heat wave.

Children cool off at a fountain in Washington D.C., the United States, on July 20, 2019. The highest temperature reached 36 degrees Celsius in Washington D.C. on Saturday as a result of a prolonged heat wave.

People cool off at a fountain in New York, the United States, on July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

People cool off at a fountain in New York, the United States, on July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.

People cool off at a fountain in New York, the United States, on July 20, 2019. New York City entered a state of emergency on Friday due to the first heat wave of this summer. The temperature in the city soared to 37 degrees Celsius on Saturday as the extremely hot air swept through.