NEW YORK, July 22 (Xinhua) -- The utility company Con Edison has restored the power supply to about 13,000 people in southeast Brooklyn in New York City (NYC), according to a statement released Monday.

Meanwhile, 40,000 people in the city are still without electricity, about 20,000 of whom are customers in Brooklyn, NYC Mayor Bill De Blasio has said.

"It's still hot and people have a right to be frustrated," De Blasio tweeted. "We're pushing Con Ed to get power back as fast as possible."

NYC entered a state of emergency on Friday due to the first heat wave of this summer, which is affecting most of the Midwest and Northeast.

The mayor said that the city's emergency management was deploying personnel on the ground in case of emergency and to ensure people's safety.

Con Edison, the utility service that has been under scrutiny since a massive blackout in Midtown and Upper West Manhattan on July 13, is "ready for what the heat will bring," said its president Tim Cawley.

In NYC, extreme heat is the number one cause of mortality from extreme weather, according to a report in 2017.