New tornado alert as Missouri twister death toll hits 122

America's battered Midwest is on tornado alert again as a massive twister bears down on Oklahoma City, reportedly killing four people and critically injuring three children.

The latest warnings come as the death toll from the massive storm that ravaged Joplin, Missouri reached 122, making it the deadliest single US twister in six decades, officials said today.

The latest twister has been described as ‘‘extremely dangerous and life threatening’’, CNN has reported, snapping power poles and overturning cars as it tore through communities.

At least two tornadoes had touched down in Oklahoma with one tornado causing an ‘‘unspecified number of deaths’’ and the other racing towards Oklahoma City, CNN said.

‘‘It appears as a big black cloud comin’ at ya over the ground,’’ a weather forecaster on TV station KFOR told viewers.

CBS reported that the twister had killed four people and critically injured three children as it raced through the outer western suburbs of Oklahoma City.

That toll from the Joplin disaster is expected to rise as rescuers work desperately to search ruined buildings.

Officials said 750 people had been treated in hospital after the twister hit on Sunday, US time, cutting a swath of destruction 6.4 kilometres long and a kilometre wide through Joplin, a town of about 50,000.

According to the National Oceanic and Atmospheric Administration (NOAA), the previous highest death toll from a single tornado was recorded in Flint, Michigan in 1953 with 116 fatalities.

Officials said the tornado ranks as the eighth deadliest in America's history.

More on Oklahoma tornado soon.