WASHINGTON (AFP) - Rescuers in the US state of Oklahoma were searching Sunday (May 26) for survivors in the tangled remains of mobile homes and other structures demolished overnight by a powerful tornado that killed at least two people.

"Right now (we are) doing a search effort to assess everything," El Reno Mayor Matt White told reporters in a televised news conference. "We can confirm there have been two fatalities at this time."

"It is very traumatic."

The city of about 17,000, 25 miles (40 kilometres) west of state capital Oklahoma City, was just recovering from serious flooding when the storm hit late Saturday with little warning.

At least 29 people were hospitalised, with injuries ranging from minor to critical.

A mobile home park was nearly flattened, and White said residents had been moved to temporary shelters.

"We do need some help," he said. "We have moved all the people out of the trailer park."

Photos showed widespread devastation, with many mobile homes mangled beyond recognition.

In addition, White said, most of the second story of a local motel, the American Budget Value Inn, was lost.

"Pray for the families," he told reporters. "People have absolutely lost everything. You're not going to believe the devastation."

The National Weather Service (NWS) office in Norman, Oklahoma tweeted that Saturday's tornado was an EF3 on the Enhanced Fujita Scale, meaning it packed winds of 136 to 165 miles per hour, making it capable of inflicting severe damage. The NWS said the storm was on the ground for 2.2 miles.

El Reno and Oklahoma City are in what is often referred to as Tornado Alley, a region frequently hammered by storms of rare intensity, particularly in spring and early summer.

A tornado on May 3, 1999 that struck parts of the capital city reached estimated wind speeds of more than 300 miles per hour (480 kilometres per hour), among the highest speeds - and with the most violent force - ever recorded anywhere.

Thirty-six people died.