At least eight people were killed Thursday night when a tourist boat capsized in a southern Missouri lake as powerful thunderstorms passed through the Midwest, the authorities said.

Stone County Sheriff Doug Rader said that the boat sank to the bottom of the lake and that seven passengers were taken to a hospital. Two people were in critical condition at Cox Medical Center Branson late Thursday. Divers were searching for missing passengers, and the sheriff said that would continue overnight.

A sheriff’s deputy was on the scene when the accident happened and was assisting in the rescue, the sheriff said.

The boat capsized because of severe weather, Rader said, adding that he believed that all the fatalities were caused by drowning.

The Southern Stone County Fire Protection District said on Facebook that 20 or more people were on the boat, and local news outlets quoted Rader as saying there were 31 people on board.

Ripley Entertainment owns the boat, having acquired the Ride the Ducks attraction in Branson last year. Duck boats can float on the water and drive on land.

Suzanne Smagala-Potts, a spokeswoman for Ripley Entertainment, said this was the first time an accident had happened at this location. “Our thoughts are first and foremost with the families,” she said.

Family members of missing people believed to have been on the boat were directed to go to Branson City Hall.

Becca Blackstone, a manager of an Irish pub in Branson, said the duck boat tours are popular with tourists, and she has ridden them four times in her decade of living there. She said the tours, which usually last from an hour to 90 minutes, take tourists to land destinations like the College of the Ozarks and then onto the lake.

“It’s just a lot of fun, normally,” she said in a phone interview. “It’s nothing like this. And with them going out in the storm, I don’t necessarily know what that’s about because it’s not like we didn’t know about this storm.”

She said that in the times she went on the duck boats, people were not required to wear life jackets, although the boat had them on board.

Blackstone said the accident was the “craziest thing” that had happened in the area since a tornado hit several years ago.

The episode was the result of a storm system that meteorologists said had passed across much of the Midwest on Thursday.

Steve Lindenberg, a meteorologist at the National Weather Service’s office in Springfield, Missouri, about 45 miles north of Branson, said a line of thunderstorms rattled the area Thursday night and produced winds of up to 74 mph. The winds downed trees and power lines, he said.

Lindenberg said a 63-mph gust was recorded at Branson’s airport around 6:55 p.m. local time, although he did not know whether the winds had caused the boat to capsize.

He said the thunderstorms had since left Missouri and moved into Arkansas.

Rod Donavon, a National Weather Service meteorologist in Des Moines, Iowa, said several tornadoes swept through the central part of that state Thursday, apparently damaging a warehouse, homes and other structures.

Two, in the cities of Pella and Marshalltown, struck within about 30 minutes of each other and were particularly destructive, Donavon said. He described them as “strong” but said the exact strength of the winds were not yet clear.

Thursday’s episode was not the first involving a duck boat to end with casualties.

In 2010, a barge plowed into a duck boat packed with tourists that had stalled on the Delaware River, sending 37 people into the water and ultimately killing two. In 1999, 13 people drowned when a duck boat sank without warning on an Arkansas lake.

The New York Times

Jacey Fortin, Julia Jacobs and Matt Stevens © 2018 The New York Times