A monstrous tornado killed at least 24 people Monday as it roared through Moore and south Oklahoma City — leaving rescue workers frantically searching into the night for missing children at the devastated Plaza Towers Elementary School in the Moore School District.

At least 20 children were included among those killed, and the death toll is expected to rise, the state medical examiner reported.

More than 100 were injured.

President Barack Obama issued a federal disaster declaration late Monday. The president’s action makes federal funding available to affected individuals in Cleveland, Lincoln, McClain, Oklahoma and Pottawatomie counties.

Oklahoma Highway Patrol trooper Betsy Randolph described the devastation as “the worst thing I have ever seen.”

“When I got to Moore, I saw a lot of walking wounded — people with blood all over. It was a matter of putting work gloves on and getting to work,” she said. “We hope that we don’t have any more fatalities, but we know there are a lot more people trapped tonight.”

Randolph urged people to stay away from the area.

The number of fatalities already has surpassed the 44 killed in the horrific May 3, 1999, tornado that previously devastated the Moore-south Oklahoma City area.

As night fell, relatives were crying out for their children at Plaza Towers, where they said more than 20 children were missing and feared dead. Emergency responders continued working late into the night in hopes of finding survivors.

Plaza Towers was one of two Moore elementary schools ravaged by the massive tornado as it ground up neighborhoods, cars and everything else in its path.

Briarwood Elementary School was the other elementary school slammed.

The gymnasium at Moore’s Highland East Junior High School also was struck, leaving football equipment strewn across the ground.

Chaos reigned at Briarwood shortly after the tornado hit as crying, mud-caked children could be seen streaming from the collapsed building.

Frantic parents rushed toward the school, dodging downed power lines and scattered debris.

What appeared to be the lifeless body of a child was pulled from the rubble of a home about four houses down from the school.

The tornado — with wind speeds preliminarily estimated at up to 200 mph — ripped the roof off the school and collapsed school walls, leaving several children trapped in the debris. Emergency workers arrived quickly on the scene and began laboring to free the children. A witness said none of the Briarwood school children he saw appeared to have major injuries.

The smell of natural gas filled the air from broken gas lines.

Emergency Medical Services Authority rushed ambulances to schools, several homes, businesses and intersections in response to reports of multiple injuries.

Later Monday, Briarwood students were taken to a location at Vicki Drive and 156 Court, where officials sought to reunite them with parents.

Southmoore High School used a bus and police squad cars to shuttle students from the school to a location where they could be reunited with their parents following the storm.

Garrett Bennett, a 15-year-old freshman, said he was in the field house with coaches and other players when the storm hit.

Coaches had about 15 students and student managers go to a locker room in the building’s interior, and at one point had them all put on football helmets, Bennett said.

“They came in and told us to get on the floor and put your head down,” he said.

Kelly Wells, Norman Regional Medical Center spokeswoman, said Moore Medical Center was significantly damaged, with the second floor largely gone.

“All of our staff has been accounted for,” she said. “None of our patients there have been critically injured. We’re in the process of evacuating the hospital.”

The hospital had 30 patients at the time. They were being taken to two Norman hospitals.

Wells said staff members told her the hospital’s second floor is “pretty much gone, and the front side is gone.” The north end of the hospital was also heavily damaged, she said.

OU Medical Center and Children’s Hospital reported treating 85 storm patients, including 65 children. Medical conditions ranged from minor to critical.

St. Anthony Hospital treated six injured patients and Integris Health Southwest Medical Center treated 55, including a 7-year-old boy whose parents could not be located. Hospital officials said they would keep him until his parents are found.