MOORE, Oklahoma (AFP) - Monday's tornado in this Oklahoma City suburb damaged or destroyed 1,200 homes and affected 33,000 people, officials said on Thursday.

Updating figures from one of the worst United States (US) tornados in recent years, they said the death toll from the powerful twister - which struck with little notice in mid-afternoon - remains at 24, with 377 injured.

"We hope and pray that those numbers will hold steady and not go up," said Governor Mary Fallin at a press conference in Moore city hall alongside law enforcement, disaster relief and other officials.

The 24 fatalities included two infants and seven pupils from Park Towers Elementary School, one of two schools in the path of the twister that cut a 27km long swath through the mainly residential city of 56,000.

No students were hurt at the other school, Briarwood Elementary.

Parts of the south side of adjacent Oklahoma City, the state capital, were also hit, but Moore took the brunt of the devastation.

Unofficial estimates of property damage have been running in the region of US$2 billion (S$2.52 billion), as insurance adjusters in the disaster zone continue to take stock of the losses.

The National Weather Service has classified the tornado as a rare EF-5 on the six-step Enhanced Fujita scale, indicating that it packed winds of 320kmh.

Three-quarters of the world's tornados strike the US in a north-south corridor stretching from the Dakotas to Texas colloquially known as Tornado Alley.

But they are typically half the strength of Monday's killer funnel, meteorologists say.

Moore has previously been hit twice by tornados in recent years, including one in May 1999 - also an EF-5 - that killed 41 people.