Story updated at 9:30 p.m. with information from sheriff's press conference. 

NEAR BRANSON, Mo. • Eight people are dead and an unknown number of others are missing after a tourist boat capsized on Table Rock Lake on Thursday night, the Stone County sheriff said.

Sheriff Doug Rader said that seven people were taken by ambulance from the scene where the Ride the Ducks boat sank.

"It capsized and sank," Rader said of the tourist boat. He said the boat remained underwater late Thursday night.

He said the dead are believed to have drowned.

He added that the disaster had apparently been caused by a powerful storm that moved through.

Rader said an off-duty deputy from his department had been on the boat when it went under. He credited the deputy with rescuing some of the boat's passengers.

"We do have some people still missing so this is going to be all night into the morning we're going to be working on this," the sheriff said.

People who had relatives on the boat were urged to go to Branson City Hall to await reports.

Officials with the Southern Stone County Fire Protection District said at about 8:20 p.m. that crews from several agencies and divers were on scene.

Fire Protection District spokesman Eric Nielsen said the boat is submerged and cannot be seen from the surface.

The fire district said the Branson Belle showboat was being used in the rescue but was not involved.

The accident reportedly happened after a severe line of thunderstorms rolled through the area. Officials noted there was "storm debris" around the area.

Late Thursday, Gov. Mike Parson tweeted: "Very sad to hear about this horrible accident — prayers for all those involved and the first responders who are assisting."

This is a breaking story. Check back for details.