Rescue crews are continuing to search for survivors in the central U.S. state of Oklahoma, where a tornado with winds of 320 kilometers an hour caused massive destruction and killed at least 51 people.
Authorities say the death toll is expected to rise. Among those killed were young children who were inside a school when the tornado hit Monday afternoon.
Large sections of Moore, an Oklahoma City suburb, were destroyed as the tornado flattened entire neighborhoods and sent debris flying through the air. At least 120 people were injured..
Rescue workers have pulled several children alive out of the rubble of two schools that were hit, while other kids remain among the missing.
Oklahoma Governor Mary Fallin told reporters that "hearts are broken'' for parents looking for their children. She deployed the state National Guard and extra police to assist with rescue operations.
President Barack Obama declared a major disaster in Oklahoma as a result of the storm. He ordered the Federal Emergency Management Agency to provide any assistance that Oklahoma needs.
Homeland Security Secretary Janet Napolitano expressed sympathy for those impacted by the storm and pledged "all available resources" to help the affected areas.
The National Weather Service said the magnitude of this tornado was an EF-4, the second most-powerful type of twister there is.
Moore, Oklahoma also was hit hard by a deadly tornado in 1999.
The tornado Monday is the deadliest in the United States since 2011, when a storm in the central community of Joplin, Missouri killed 161 people.