Obama assures all federal support to tornado-hit Oklahoma

US President Barack Obama today assured full federal support to Oklahoma City, where many areas have been devastated following the monstrous tornado that hit the region, leaving at least 91 people dead.

"As a nation, our full focus right now is on the urgent work of rescue and the hard work of recovery and rebuilding that lies ahead," the US President said in his brief address to the nation this morning following yesterday's deadly storm.

As has been the case with all major natural disasters and tragic events during his presidency, Obama was personally monitoring the rescue and relief operations and was frequently updated by his top officials.

Overnight he declared a State of Emergency for Oklahoma so as to facilitate quick federal aid and this morning he spoke with the Mayor of Moore, the worst-hit town.

With wind speeds of over 320 kilometres per hour, the tornado, said to be more than a mile-wide caused widespread devastation in parts of Oklahoma.

The worst-hit was a pair of schools where children had taken shelter. The schools were reduced to a pile of rubble as the tornado crossed Moore town.

"I've met with (Homeland Security) Secretary (Janet) Napolitano this morning and my homeland security and counter-terrorism adviser, Lisa Monaco, to underscore that point that Oklahoma needs to get everything that it needs right away," Obama said.

"The Federal Emergency Management Agency (FEMA) administrator Craig Fugate is on his way to Oklahoma as we speak. FEMA staff was first deployed to Oklahoma's emergency operations centre on Sunday, as the state already was facing down the first wave of deadly tornadoes," he said.

Local officials said they fear an increase in death toll as the rescue operation was still ongoing and the first responders were still looking for signs of life under the pile of rubble. More than 100 people have been rescued so far. Among the dead include at least 20 children while a major hospital has been badly damaged.

"Our hospital has been devastated. We had a two-storey hospital, now its one-storeyed. And it's not occupiable," Moore City Mayor Glenn Lewis told CNN. Local media reported the city resembled a war zone.