Tornadoes were seen in different parts of the city of 485,000 on Friday but one particularly devastating column of air struck the Elkhorn area, damaging house roofs and structures.
Police and firefighters moved door-to-door to help people. Crews went to the "hardest hit area" and had a plan to search anywhere someone could be trapped, Omaha fire chief Kathy Bossman said.
"They're going to be putting together a strategic plan for a detailed search of the area, starting with the properties with most damage," Ms Bossman said.
"We'll be looking throughout properties in debris piles, we'll be looking in basements, trying to find any victims and make sure everybody is rescued who needs assistance."
Elkhorn resident Patrick Woods said: "When we came up, our fence was gone and we looked to the northwest and the whole neighbourhood's gone.”
His wife Kim added: “The whole neighbourhood just to the north of us is pretty flattened."
The tornado warning was issued in the Omaha area on Friday afternoon just as children were due to be released from school.
Many schools had student shelters in place until the storm passed. Hours later, buses were still transporting students home.
Another tornado hit an area on the eastern edge of Omaha, passing directly through parts of Eppley Airfield, the city's airport.
Officials closed the airport to aircraft operations to assess damage but then reopened the facility.
After passing through the airport, the tornado crossed the Missouri River and into Iowa, north of Council Bluffs.
In Lancaster County, where three people were injured when an industrial building collapsed, sheriff's officials also said they had reports of a tipped-over train near Waverly.
The Omaha public power district reported that nearly 10,000 customers were without power in the Omaha area.
The forecast for Saturday was ominous. The weather service issued tornado watches across parts of Iowa, Kansas, Missouri, Oklahoma and Texas. And forecasters warned that large hail and strong wind gusts were possible.
