Oklahoma tornado: Amateur storm chasers' smartphone footage of cyclone

The terrifying tornado which ripped through Oklahoma and Kansas has been captured on film by dozens of amateur storm chasers and eyewitnesses alike.

Over the past two days dramatic smartphone videos have emerged of the vast weather system swirling towards towns, schools and neighborhoods.

At least four tornadoes swept through Oklahoma, while Kansas and Iowa were also hit hard by a massive storm system that stretched from Texas to Minnesota.

[Weather reporter flees studio live on air as tornado hits]

At least four separate tornadoes touched down in Oklahoma, including the one near the town of Shawnee that laid waste to much of a mobile home park.

Amateur videos which emerged online show eyewitnesses caught in an apparent dilemma over whether to continue filming the swirling clouds or run for cover.

Reports of injuries in that tornado strike could not immediately be confirmed, as getting into the area was made difficult by the overturned tractor-trailers that forced the closure of a section of a highway.

[Pictures and video: Up to 91 people killed in Oklahoma tornado]

A storm spotter told the National Weather Service that the tornado left the earth "scoured" at the mobile home park.

Forecasters had been warning for days that the weekend storm system could produce tornadoes, and the emergency services throughout the region were keeping a close eye on it last night as it moved north-east.

Tornado watches or warnings were in effect in several states.

[Oklahoma tornado: Live updates]

Dozens of homes were damaged by the other tornadoes that touched down in Oklahoma, but emergency officials had no immediate reports of injuries caused by any of them.

In Wichita, Kansas, a tornado knocked out power to thousands of homes and businesses but bypassed the most populated areas of the state's biggest city.

More pictures as Oklahoma is devastated by terrifying tornado: