Texas has begun what is being described as the biggest search and rescue effort in its history following Hurricane Ike.
At least 2,000 people have been rescued but many thousands more are believed to have ignored the mandatory order to evacuate before Saturday's storm.
The death toll rose to 30 as Ike swept on from Texas into the mid-US, with heavy rain causing flooding.
Millions of people are without power and Houston is under a week-long curfew as work continues to restore services.
While many schools remained shut, there were signs of a return to normality on Monday, as the city's two airports resumed limited services and some shops and restaurants opened for business.
Five people died in Galveston Bay, an island city south-east of Houston which bore the brunt of the storm as Ike swept ashore on Saturday, bringing 13ft (4m) waves and 110mph (175km/h) winds.
Rescuers feared the toll could rise as they searched areas awash with sewage for those who did not leave before the hurricane hit.
As many as 140,000 people - some 10,000 in Galveston alone - failed to heed the order to evacuate.
Across Texas, 50 helicopters, 1,500 federal, state and local search teams were looking for stranded survivors, and a US navy ship carrying engineers was heading to Galveston to help with rebuilding operations.
We'll work as hard and fast as we can to help you get your lives back up to normal
Nearly 40,000 evacuees were being housed in 250 shelters across Texas - some with little money and no idea how long they would have to stay.
Galveston Mayor Lyda Ann Thomas urged residents to stay away until it was safe to return to their homes.
"There's nothing to come here for," she said. "Please leave."
Warning that residents of Texas and Louisiana were in for "tough times", David Paulison, administrator of the Federal Emergency Management Agency (Fema), said some people would "be out of their homes for not only weeks, but months".
Fema has said it will deliver 7.5m meals as well as 5m gallons (20m litres) of water over the next few days.
President George W Bush, who is due to survey the damage on Tuesday, told those affected by the storm: "We'll work as hard and fast as we can to help you get your lives back up to normal".
Although Ike weakened to a tropical depression as it headed beyond Texas, the storm's US death-toll rose to 30 as torrential rain caused severe flooding and power outages in parts of Louisiana, Kansas, Missouri and Illinois.
Ike killed more than 80 people when it tore through the Caribbean late last week.
Have you been affected by Hurricane Ike? Send us your comments and experiences using the form below.
The BBC may edit your comments and not all emails will be published. Your comments may be published on any BBC media worldwide.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.