The weather wasn't cooperating with their efforts: National Weather Service crews surveying the damage in Moore reported rain, half-inch hail and 45-mph winds over the debris field.
The Oklahoma Highway Patrol asked motorists to steer clear of Interstate 35 near Moore to free up lanes for disaster response resources streaming into the area.
And so many people were showing up to volunteer that authorities had to plead with would-be rescuers to stay away.
Path of devastation
The storm struck near Newcastle, Oklahoma, at 2:56 p.m. Monday -- 16 minutes after the first warnings went out, according to the National Weather Service.
Moore residents had another 30 to 40 minutes before the massive storm entered the western part of the city, CNN meteorologist Sean Morris said.
As Fallin had said Monday night, Lamb said he believed residents had time to prepare for the storm.
"My understanding is that the warning system was good. It was adequate," he said.
Among the many buildings struck by the storm were two schools: Plaza Towers and Briarwood elementaries.
About 75 students and staff members were hunkered down in Plaza Towers when the tornado struck, CNN affiliate KFOR reported.
At one point, an estimated 24 children were missing from the school, but some later turned up at nearby churches.
On Monday, a father of a third-grader still missing sat quietly on a stool outside. Tears cascaded from his face as he waited for any news.
Even parents of survivors couldn't wrap their minds around the tragedy.
"I'm speechless. How did this happen? Why did this happen?" Norma Bautista asked. "How do we explain this to the kids? ... In an instant, everything's gone."
Across town, Moore Medical Center took a direct hit.
"Our hospital has been devastated," said Lewis, the Moore mayor. "We had a two-story hospital, now we have a one. And it's not occupiable."
So 145 of the injured were rushed to three other area hospitals.
That number includes 45 children taken to the children's hospital at Oklahoma University Medical Center, Dr. Roxie Albrecht said. Injuries ranged from minor to severe, including impalement and crushing injuries.
'Cars crumpled up like little toys'
The National Weather Service pegged the tornado's winds at about 190 mph, placing it at the upper end of the EF4 category, the second-most powerful category of storm.
But Rick Smith, a meteorologist for the weather service, told reporters Tuesday that number could go higher.
Weather service assessment crews were just making their way into the most heavily devastated areas Tuesday afternoon, he said.
"We've seen numerous structures that are wiped clean to the foundation." Smith said.
State Highway Patrol Trooper Betsy Randolph told CNN affiliate KOKI that it was "mass devastation."
"I'm talking everywhere you looked, the debris field was so high, and so far and so wide, wounded people walking around the streets," she said. "They were bloody; there were people that had stuff sticking out of them from things that were flying around in the air. There were cars crumpled up like little toys and thrown on top of buildings. Buildings that were two and three stories tall that were leveled."