The vessel was carrying about 30 people on Table Rock Lake, a popular tourist attraction near the town of Branson, when it capsized, local media say.
Rader said divers were on the scene searching for passengers, but could not confirm how many were missing.
"The Ducks have a ramp access where they put in, and when the wind hit it pushed the boat right square behind the Branson Belle", Pulley said.
Rader said weather is believed to have caused the boat to capsize. Seven other people were being treated at hospitals, he said, and search operations remained under way for the rest.
So this is going to be an all night, into tomorrow [search],' Stone County Sheriff Doug Rader told reporters about 9.30pm.
He also said an off-duty sheriff's deputy working security for the boat company helped rescue people after the accident.
A thunderstorm rolled through Branson between 7 and 7:30 p.m., with wind gusts as high as 63 miles per hour. The winds were likely stronger over the lake, Linderberg said.
In a telephone interview with witness Mandi Rogers, she said the boat is a tourist attraction in the area.
We will continue to bring you updates as more information becomes available.
Missouri Gov. Mike Parson addressed the incident on Twitter late Thursday, offering his "prayers for all those involved".
This is a developing story.