Gov. Greg Abbott (R-TX) said around 24,000 National Guard members would be deployed throughout Texas, with about 10,000 Guard members coming from other states.

On Monday, Abbott activated all 12,000 members of the Texas Military Department, which is the state’s agency that houses the Texas Army, Air, and State Guards. Tuesday, Gen. Joseph Lengyel, the chief of National Guard Bureau, said a dozen other states may get involved. As of yesterday, that help included around 346 Air Guard members, four planes, and three helicopters from at least seven states.

Officials estimate around 30,000 residents will be forced from their homes. But the weather may complicate missions to save them. High winds sometimes make it hard for the rescuers to fly. They occasionally have to suspend missions because of those harsh conditions. But a spokesperson from the Texas Military Department tells Vox ground operations continue because they have big trucks that can drive through flooded streets.

The US Coast Guard, which falls under the US Department of Homeland Security, is also rescuing people in Houston. So far, the Coast Guard has rescued more than 4,500 people, a Coast Guard spokesman told Vox.

Harvey is now an historic rainstorm that dropped around 19 trillion gallons of water in Texas, and has reached more than 50 inches in some parts of the Houston area. “Pending final confirmation, these would be the heaviest storm totals from any tropical cyclone in the continental U.S. in records dating to 1950,” the Weather Channel reports.

That’s led to devastating floods and storm-related complications that killed at least 20 people, a number that’s expected to rise. “The worst is not yet over for southeast Texas as far as the rain is concerned,” Abbott told reporters today.

Interstate 10 at the Jefferson / Chambers county line. Waves with white caps on the interstate. #Harvey pic.twitter.com/GH79zIoQAk — Dade Phelan (@DadePhelan) August 30, 2017

“The threat of heavy rains has ended in the Houston/Galveston area,” the National Hurricane Center advised this morning. “However catastrophic and life threatening flooding will continue in and around Houston, Beaumont/Port Arthur, eastward into southwest Louisiana for the rest of the week.”

Houston’s mayor, Sylvester Turner, imposed a curfew from midnight to 5 am, to prevent looting. “There are some who might want to take advantage of this situation, so even before it gets a foothold in the city, we just need to hold things in check,” Turner told reporters.