At least nine people were killed across the central United States as tornadoes and other extreme storms hit several states including Texas, Arkansas and Oklahoma, officials said Sunday.

Rescue efforts were ongoing and hundreds of thousands of people were without power after the storms struck the Southern Plains region beginning late Saturday.

In Texas, Cooke County Sheriff Ray Sappington told ABC affiliate WFAA that five people were dead after a tornado ripped through the Valley View area, north of Dallas.

"Sadly, I think that number will rise," Sappington told The Weather Channel, adding that search and rescue operations were ongoing.

The twister destroyed homes and a gas station, and overturned vehicles on an interstate highway. Sappington called the damage "pretty extensive."

There had been "a lot" of injuries, though none there were life-threatening, he earlier told ABC affiliate WFAA.

In Oklahoma, at least two people were dead after a tornado hit Mayes County late Saturday, the county head of emergency management Johnny Janzen told the Fox News affiliate in Tulsa.

And in northern Arkansas, two people were killed in storms in the early hours of Sunday, local authorities confirmed.

As far north as Indiana, the start of the Indianapolis 500 was delayed Sunday due to storms in the area, with fans asked to exit the bleachers and seek shelter.

A crowd of 125,000 was expected for the race, one of the most emblematic car races in America.

As the storm system moved across the country, some 470,000 people were without power in states stretching from Texas to Kansas, Missouri, Arkansas, Tennessee, and Kentucky, according to the website Poweroutage.us.

Tornado alerts were still active in several places.