May 17 (UPI) – Four people were killed when severe storms hit the Houston area on Thursday, authorities said, warning people to stay home.

Storms with wind speeds of up to 100 mph hit the Texas city on Thursday, causing major damage, officials said during a news conference.

Houston Mayor John Whitmire urged the public to stay home Thursday night and Friday as only essential workers would be allowed to go to work. Schools would also remain closed.

“Stay home tonight,” he said. “If you’re not an essential worker, don’t go to work tomorrow.”

The public is advised to avoid the city center because, according to authorities, there has been significant storm damage there.

“Please do not drive to downtown Houston or other areas in the region affected by storm damage this evening,” the National Weather Service Houston reiterated in an online statement late Thursday.

“Debris, broken glass and power lines are scattered across the streets.”

Houston Fire Chief Samuel Pena said two of the deaths were due to fallen trees and a third was due to a crane accident. The cause of the fourth death was not disclosed.

The fast-moving storms knocked out power to nearly a million homes, according to poweroutage.us. Whitmire said it would take 24 hours for most homes to get back online, while others would be without power for up to two days.

“We are responding to a large number of power outages caused by severe weather in portions of our service area,” CenterPoint Energy said in a statement. “Please be prepared for extended weather-related power outages and possible delays in some outage notifications.”