At least seven people have been killed as a string of violent thunderstorms battered middle-America, with several tornadoes touching down in Oklahoma and high winds pounding rural Kansas.
Tuesday's 'supercell' storms came just two days after a massive tornado tore through the southwest Missouri town of Joplin, killing at least 123 people and injuring hundreds more, according to authorities.
Supercell thunderstorms are characterised by the presence of a deep, continuously-rotating updraft.
Several tornadoes struck Oklahoma City and its suburbs during rush hour on Tuesday, killing at least five people and injuring dozens more, including three children who were in critical condition, authorities said.
In Kansas, police said two people died when high winds threw a tree into their van near the small town of St John, about 160km west of Wichita. The highway was shut down because of storm damage.
More severe weather was expected as the storms continued east.
"Unfortunately, this event will likely continue for some time," Oklahoma governor Mary Fallin said. "I am asking all Oklahomans to stay aware of the weather and to take proper precautions to keep themselves out of harm's way."
The line of storms began about 3pm in Oklahoma and followed tracks greater than 65km into the state's capital city before continuing on towards Tulsa. Oklahoma state offices and many businesses let workers leave hours earlier to get out of harm's way.
Storm clouds also spawned funnel clouds and at least one tornado around North Texas, but there were no immediate reports of damage or injuries.
Rescue crews in the Midwestern US city of Joplin in Missouri rummaged through piles of debris, searching for survivors of a massive tornado that killed 123 people and wreaked havoc in the city.
Barack Obama, the US president, said he was "heartbroken" over the devastation wrought by the storm over the weekend and would visit the disaster zone on Sunday, following his four-nation visit to Europe.
"Our thoughts and prayers are with the families that are suffering at the moment," Obama told reporters in London, after earlier promising federal aid for recovery efforts.
"All we can do is let them know that all of America cares deeply about them and we are going to do absolutely everything we can to make sure they can recover," he said.
At least 750 people were also injured in the twister that damaged or destroyed more than 2,000 buildings - or about a third of Joplin. Many of those wounded were reported to have massive internal injuries, according to local officials.
Al Jazeera's Rob Reynolds, reporting from the scene of the disaster in Joplin, said the death toll could still rise since some areas had not yet been searched by rescue teams.
The tornado struck the city near the border with Oklahoma and Kansas on Sunday evening, less than a month after a horrific tornado outbreak left 354 dead across seven US states.
The twister was the deadliest of 46 tornadoes reported to the National Weather Service in seven states on Sunday.