Severe thunderstorms hit southeastern Texas on Thursday for the second time this month, killing at least four people.

The storms blew out windows in high-rise buildings, downed trees and knocked out power to nearly 900,000 homes and businesses in the Houston area.

Mary Benton, chief of communications and senior advisor to the mayor, confirmed the four deaths.

Flash flood and severe thunderstorm warnings were issued for multiple counties, with damaging winds and even tornadoes possible into the evening, Houston’s National Weather Service (NWS) office said.

“Take shelter now if you’re in the path of this storm. Head to the lowest floor!” the NWS office said on social media.

Streets were flooded, and trees and power lines were down across the region. KHOU-TV showed images of shattered windows on an office building in downtown Houston, with glass littering the street below.

City officials urged residents to stay off the roads as many were impassable and traffic lights were out.

Flights were grounded at Houston’s two major airports because of the weather. Sustained winds topping 60 mph were recorded at Bush Intercontinental Airport.

More than 870,000 customers were without electricity in and around Harris County, which contains Houston, according to poweroutage.us. The county is home to more than 4.7 million people.

The Houston Independent School District cancelled classes on Friday for all its 274 campuses.

Heavy storms slammed the region during the first week of May, leading to numerous high-water rescues, including some from the rooftops of flooded homes.