A deadly tornado since Monday tore through a town in the US state of Oklahoma, destroying two schools and killing up to 24 people, including at least seven children, and injuring over 200.

US rescue teams launched a massive hunt for survivors Tuesday after a tornado tore through a suburb of Oklahoma city, causing chaos and leaving dozens dead.

State medical examiner's office spokeswoman Amy Elliott said 24 victims had been confirmed dead. Earlier reports had cited higher tolls which were later revised down, and the number is expected to rise as recovery efforts continue.

The 3-kilometer wide tornado tore through the town of Moore outside Oklahoma City, trapping victims beneath the rubble as two elementary schools were heavily damaged.

Oklahoma City lies inside the so-called "Tornado Alley" stretching from South Dakota to central Texas, an area  vulnerable to tornadoes.

The storm flattened block after block of homes, setting off fires, downing power lines and tossing cars across a miles-wide swath of destruction that recalled some of the worst US natural disasters of the last decade.

At least 101 people have been pulled alive from under debris, said Terri Watkins, spokeswoman for the Oklahoma Department of Emergency Management. President Barack Obama declared a major disaster area in Oklahoma, ordering federal aid to supplement state and local efforts in Moore after the deadliest US tornado since one killed 161 people in Joplin, Missouri in 2011.

The National Weather Service assigned the twister a preliminary ranking of EF4, indicating that it packed winds of 166 to 200 miles per hour (267-322 km/h), more severe than a category five hurricane.

The Moore Medical Center was evacuated after it sustained damage, and state authorities called out the National Guard to help rescue efforts as Obama ordered federal aid to supplement local recovery efforts. Rescue operations could be hindered by more bad weather on the way.

Agencies