Police and firefighters worked around the clock, looking for survivors.
"We're in that critical time that people can be rescued," Chief Pat Sullivan said on CBS News' The Early Show. "If we don't get out thereto and do it now, then they're going to die."
The Federal Emergency Management Agency's Deputy Director Patrick Rhode told CBS News Correspondent Peter Maer the current mission in the region centers on lifesaving, as crews continue the search for survivors. He called it a "very aggressive search and rescue effort" and warned "the storm is just as dangerous after the storm as it was during" the disaster. He cautioned that people should not even think about returning to their homes.
A helicopter view of the devastation over Mississippi revealed people standing on black rooftops, baking in the sunshine while waiting for rescue boats.
"I can only imagine that this is what Hiroshima looked like 60 years ago," said Mississippi Gov. Haley Barbour after touring the destruction by air Tuesday.
One Mississippi county alone said it had suffered at least 100 deaths, and officials are "very, very worried that this is going to go a lot higher," said Joe Spraggins, civil defense director for Harrison County, home to Biloxi and Gulfport. In neighboring Jackson County, officials said at least 10 deaths were blamed on the storm.
Several of the dead in Harrison County were from a beachfront apartment building that collapsed under a 25-foot wall of water as Hurricane Katrina slammed the Gulf Coast with 145-mph winds Monday. Louisiana officials said many were feared dead there, too, making Katrina one of the most punishing storms to hit the United States in decades.
Many Mississippi residents remained without electricity, some without clean drinking water. Officials said it could be weeks, if not months, before most evacuees will be able to return.
Emergency medical teams from across the country were sent into the region and President Bush cut short his Texas vacation Tuesday to return to Washington to focus on the storm damage.
In devastated Biloxi, areas that were not underwater were littered with tree trunks, downed power lines and chunks of broken concrete. Some buildings were flattened.