NATIONAL NEWS (CNN) — At least 51 people -- including at least 20 children -- were killed when a massive tornado struck an area outside Oklahoma City on Monday afternoon, officials said.
Seven of those children were killed at Plaza Towers Elementary School in Moore, Oklahoma, according to a police official.
Early Tuesday, emergency personnel continued to scour the school's rubble -- a scene of twisted I-beams and crumbled cinder blocks.
The tornado was estimated to be at least two miles wide at one point as it moved through Moore, in the southern part of the Oklahoma City metropolitan area, KFOR reported.
The preliminary rating of the tornado was at least EF4 (166 to 200 mph), the National Weather Service said.
-- The storm system behind Monday's twister and several on Sunday is threatening a large swath of the United States on Tuesday, putting 53 million people at risk of severe weather. In the bull's-eye Tuesday are parts of north-central Texas, southeastern Oklahoma, and northern Arkansas and Louisiana, according to the National Weather Service.
-- Oklahoma first and foremost needs donations to rebuild after tornadoes slammed the state, Gov. Mary Fallin told CNN on Tuesday.
-- More than 40,000 customers remain without power Tuesday after a powerful tornado slammed the Oklahoma City region, a utility spokesman said. More than half of those customers were in the heavily damaged suburb of Moore, according to Brian Alford, a spokesman for Oklahoma Gas & Electric.
-- Glenn Lewis, the mayor of tornado-ravaged Moore, Oklahoma, told CNN on Tuesday the rescue effort is continuing and "we're very optimistic we might find one or two people."
-- Personnel have rescued 101 people from rubble in metropolitan Oklahoma City after a tornado hit the area Monday, Oklahoma Department of Emergency Management representative Terri Watkins said Tuesday morning. Watkins cited an Oklahoma Highway Patrol tally of rescues from all agencies.
-- Some of the children killed at Plaza Towers Elementary School in Moore, Oklahoma, during Monday's storm drowned in a basement area there, Oklahoma Lt. Gov. Todd Lamb told CNN Tuesday morning. "My understanding, this school ... Plaza Towers, they had a basement. Quite frankly, don't mean to be graphic, but that's why some of the children drowned, because they were in the basement area," he said. Officials have said the storm killed at least seven children at the school.
-- The Oklahoma Medical Examiner's Office has been told to expect about 40 additional bodies, including about 20 children, according spokeswoman Amy Elliott. The official death toll of 51 will not rise until the bodies are processed, she said. The current toll already includes at least 20 children who were killed by the storm.
-- At least 145 people have been hospitalized in the Oklahoma City, hospital officials said. The Children's Hospital at OU Medical Center received 45 children for treatment on Monday, according Dr. Roxie Albrecht.
-- President Barack Obama will make a statement at approximately 10 a.m. ET after he is briefed on the aftermath of the Oklahoma tornado devastation, a White House official told CNN. The statement will be delivered in the State Dining Room.
-- Obama signed a disaster declaration for Oklahoma on Monday night, a White House statement said. The declaration means federal emergency aid will supplement local recovery efforts.
-- The president told the Oklahoma governor that the federal government "stands ready to provide all available assistance" as part of the response to a series of deadly storms that have struck the Oklahoma City area, including Monday's devastating tornado.
-- Queen Elizabeth II sent her condolences to those affected by Monday's massive deadly Oklahoma tornado, saying on Twitter: "Our deepest sympathies go out to all those whose lives have been affected, as well as the American people #Oklahoma #tornado."
-- Pope Francis urged people to join him in praying for the families of those who died in the massive tornado in central Oklahoma on Monday, "especially those who lost young children," he said in a tweet Tuesday.
-- French President Francois Hollande expressed his grief over the casualties caused by the ferocious Oklahoma tornado and saluted the "mobilization" of citizens who tackled "this exceptional situation with courage and determination."
-- German Chancellor Angela Merkel passed along her condolences to President Obama over the casualties and destruction caused by the mammoth tornado that tore through Oklahoma on Monday. "The pictures of this catastrophe render us speechless and can only hint at the scope of the hurt," Merkel told the president Tuesday.
- Pakistan and Spain issued condolences to the people affected by the deadly Oklahoma tornado. "We are particularly grieved over the loss of innocent children and their teachers who were buried under the rubble," the Pakistan government said. The Spanish government said "the Spanish people, at these tragic times, feel even closer to the American people, and share their pain."
CNN's AnneClaire Stapleton contributed to this report.