At least ninety one people, including twenty children, have died after a huge tornado tore through Oklahoma City suburbs.

Worst hit was Moore, a suburb of about 55 000 people, south of the city, where entire neighborhoods were flattened and schools destroyed by winds of up to 200mph (320km/h), according to the National Weather Service (NWS). The tornado remained on the ground for about 45 minutes.

About 200 people are being treated in hospitals.

The BBC reports Tuesday that President Barack Obama has declared a major disaster in Oklahoma and ordered the federal authorities to join in the search and recovery efforts which are continuing throughout the night.

Plaza Towers Elementary school took a direct hit: the storm tore off the building's roof and knocked down walls.

"The school was flattened. The walls were pancaked in. There's still roughly two dozen children that are missing. There have been some bodies recovered from that school and it's absolutely horrific and devastating," Oklahoma's Lt Gov Todd Lamb told the BBC.

Another school nearby - Briarwood Elementary - was also damaged, and teachers were later seen leading pupils out to safety.

Oklahoma Gov Mary Fallin is quoted saying that it was a "tragic" day.

More than 200 Oklahoma National Guardsmen as well as out-of-state personnel have been called in to assist the search-and-rescue effort.