The Oklahoma Medical Examiner's Office confirmed the nine fatalities, which included two children and seven adults. The previous overall total was seven deaths.
Local hospitals in the area reported receiving at least 89 patients, with four in critical condition. The storms hit Friday night at rush hour. The National Weather Service reported multiple tornadoes rolled in from the prairie, flipping trucks and leaving cars in floodwaters up to 4 feet deep.
Oklahoma police confirmed to ABC News that a mother and her baby were among those who died in the brutal storm. Authorities believe they were possibly sucked out of their cars near Interstate 40, a major artery connecting suburbs east and west of the city.
The latest storm hit just 11 days after a massive top-of-the-scale EF5 tornado struck Moore, Okla., killing 24 people and flattening neighborhoods.
About 125,000 power outages were reported statewide, with 95,618 just in the Oklahoma City metro area. Flash flooding warnings were in effect for central and eastern Oklahoma on Saturday.
Also Saturday morning, Will Rogers World Airport was slowly reopening and some flights were resuming, but the airport reported significant damage to the roof of the terminal, and flooding damage to walls, counters and floors.
In Missouri, the combination of high water and fallen power lines closed dozen of roads, snarling traffic on highways and side streets in the St. Louis area.
The U.S. averages more than 1,200 tornadoes a year and most are relatively small. Of the 60 EF5 tornadoes to hit since 1950, Oklahoma and Alabama have been hit the most - seven times each.
National Weather Service meteorologists said Saturday that it's unclear how many tornadoes touched down as part of the Friday evening storm system. Dozens of tornado warnings were issued for central Oklahoma and parts of Missouri, especially near St. Louis, they said, but crews must assess the damage before determining whether it was caused by tornadoes or severe thunderstorms.
ABC News and The Associated Press contributed to this report.