More than 60 military aircraft are involved in the Harvey disaster response effort, and the Navy is making preparations to send ships.
At the same time, Texas Gov. Greg Abbott activated all of the state's National Guard, resulting in about 12,000 troops available in the state. There also are troop units from other states, including Arizona, California, Nebraska, New Mexico, New York, Kentucky and Oklahoma, among others.
The U.S. Air National Guard also has aircraft and troops assisting in urban search and rescue efforts in Houston, the nation's fourth largest city. The National Weather Service is forecasting more rain and river flooding for the next few days from what is now a mega tropical storm.
"Continuing rainfall from the hurricane is expected to cause devastating and life-threatening flooding throughout this week," Army Col. Robert Manning told the media in a briefing Monday.
The state and federal response to the disaster also includes emergency supplies, including food, water, medical and other supplies. President Donald Trump is scheduled to visit Texas on Tuesday to see some of the damage firsthand.
The U.S. Coast Guard, which operates under Department of Homeland Security, had at least 20 helicopters operating earlier in the day in the greater Houston area and reported that air and ground teams had rescued more than 1,450 people by 2 p.m. ET.