A line of violent thunderstorms roared across middle America, killing six people in two states, with several tornadoes touching down in Oklahoma and high winds pounding rural Kansas.
The storms arrived as forecast, just two days after a massive tornado tore through the south-west Missouri town of Joplin and killed at least 122 people.
Several tornadoes struck Oklahoma City and its suburbs during yesterday's rush hour, killing at least four people and injuring at least 60 others, including three children who were in a critical condition.
Cherokee Ballard, a spokeswoman for the state medical examiner, said four people died west of Oklahoma City in Canadian County, where a weather-monitoring site in El Reno recorded 151mph winds.
In Kansas, police said two people died when high winds threw a tree into their van near the small town of St John, about 100 miles west of Wichita. The highway was shut down because of storm damage.
More severe weather was expected today 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 at about 3pm in Oklahoma and followed tracks greater than 40 miles into the state's capital city before continuing on towards Tulsa. Oklahoma state offices and many businesses let workers leave early 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.
In Missouri, rescuers moved from one enormous debris pile to another, racing to respond to any report of a possible survivor.
As Joplin's death toll rose to at least 122, with nine survivors pulled from the rubble, searchers raced against the clock because anybody still alive after the deadliest single tornado in 60 years was losing precious strength two days after the disaster.
For Milissa Burns, hope was fading that her 16-month-old grandson, whose parents were both taken to hospital after the twister hit their house, would be found.
She arrived at a demolished dentist's office near the family's home to watch a search team. At one point a dog identified possible human remains, prompting eight searchers to dig frantically, but they came away with nothing. Ms Burns was weary but composed, but her daughter - the boy's aunt - sobbed next to her.
"We've already checked out the morgue," Ms Burns said. "I've called 911 a million times. I've done everything I can do. He was so light and little. He could be anywhere."
The National Weather Service announced that the twister that crippled Joplin on Sunday was an EF-5, the strongest rating assigned to tornadoes, with winds of more than 200mph. Scientists said it appeared to be a rare "multi-vortex" tornado, with two or more small and intense centres of rotation orbiting the larger funnel.
It was the deadliest single twister since the weather service began keeping official records in 1950 and the eighth-deadliest in US history.
Authorities said an estimated 750 people were hurt and an unknown number were still unaccounted for.