"There's a pretty good chance some of these were a mile wide, on the ground for tens of miles and had wind speeds over 200 mph," he said.
The loss of life is the greatest from an outbreak of U.S. tornadoes since April 1974, when the weather service said 315 people were killed by a storm that swept across 13 Southern and Midwestern states.
Brooks said the tornado that struck Tuscaloosa could be an EF5 — the strongest category of tornado, with winds of more than 200 mph — and was at least the second-highest category, an EF4.
Search and rescue teams fanned out to dig through the rubble of devastated communities that bore eerie similarities to the Gulf Coast after Hurricane Katrina in 2005, when town after town lay flattened for nearly 90 miles.
In Phil Campbell, a small town of 1,000 in northwest Alabama where 26 people died, the grocery store, gas stations and medical clinic were destroyed by a tornado that Mayor Jerry Mays estimated was a half-mile wide and traveled some 20 miles.
"We've lost everything. Let's just say it like it is," Mays said. "I'm afraid we might have some suicides because of this."
President Barack Obama said he would travel to Alabama on Friday to view storm damage and meet Gov. Robert Bentley and affected families. Late Thursday he signed a disaster declaration for the state to provide federal aid to those who seek it.
As many as a million homes and businesses there were without power, and Bentley said 2,000 National Guard troops had been activated to help. The governors of Mississippi and Georgia also issued emergency declarations for parts of their states.
"We can't control when or where a terrible storm may strike, but we can control how we respond to it," Obama said. "And I want every American who has been affected by this disaster to know that the federal government will do everything we can to help you recover and we will stand with you as you rebuild."
The storm prediction center said it received 164 tornado reports around the region, but some tornadoes were probably reported multiple times and it could take days to get a final count.
In fact, Brooks said 50 to 60 reports — from the Mississippi-Alabama line, through Tuscaloosa and Birmingham and into Georgia and southwestern Tennessee — might end up being a single tornado. If that's true its path would be one of the longest on record for a twister, rivaling a 1925 tornado that raged for 219 miles.
Brooks said the weather service was able to provide about 24 minutes' notice before the twisters hit.
"It was a well-forecasted event," Brooks said. "People were talking about this week being a big week a week ago."
Gov. Bentley said forecasters did a good job alerting people, but there's only so much they can do to help people prepare.
Carbin, the meteorologist, noted that the warning gave residents enough time to hunker down, but not enough for them to safely leave the area.
"You've got half an hour to evacuate the north side of Tuscaloosa. How do you do that and when do you do that? Knowing there's a tornado on the ground right now and the conditions in advance of it, you may inadvertently put people in harm's way," he said.
Officials said at least 13 died in Smithville, Miss., where devastating winds ripped open the police station, post office, city hall and an industrial park with several furniture factories. Pieces of tin were twined high around the legs of a blue water tower, and the Piggly Wiggly grocery store was gutted.
"It's like the town is just gone," said 24-year-old Jessica Monaghan, wiping away tears as she toted 9-month-old son Slade Scott. The baby's father, Tupelo firefighter Tyler Scott, was at work when the warning came on the TV.
"It said be ready in 10 minutes, but about that time, it was there," Monaghan said. She, Slade and the family's cat survived by hiding in a closet.
- IS attack on Afghan protest kills 80 people,...
- Penny-farthing owner keeps on riding
- Scientists work toward storing digital...
- Hacked emails show Democratic party hostility...
- 'These are tough times ... but we're...
- Warner Bros. calms fans with fun 'Justice...
- A title and ship for new 'Star Trek' series:...
- New artificial reef is sunk off Florida's...
- Sarah Silverman: Bernie-or-bust Dems... 49
- Is Bernie Sanders an atheist? 43
- Trump says Russia should find Clinton's... 41
- Clinton wins historic nomination,... 37
- After turmoil, Sanders, Michelle Obama,... 31
- Obama boosts Clinton: Carry her like... 31
- Dems' division, emails roil party on... 28
- Watch live at the Democratic National... 25