(This post was last updated at 11:45 p.m. ET.)
A massive tornado ripped through the southern suburbs of Oklahoma City, Monday afternoon, killing at least 51 people, according to the state medical examiner's office.
The death toll was expected to rise.
Helicopter images showed large tracts of Moore, Okla., completely leveled by what the National Weather Service says was at least an EF-4 tornado with winds in excess of 166 mph. The tornado stayed on the ground for 40 minutes and traveled 20 miles.