Washington: Authorities say 11 people died after a duck boat carrying about 31 passengers capsized on Thursday on Table Rock Lake near the tourist town of Branson, Missouri.

Some of the dead passengers were children, Stone County sheriff Doug Rader told reporters late on Thursday night. Seven people were transported to the hospital. Of those, one sustained serious injuries, Rader said.

Search efforts for survivors halted overnight but were scheduled to continue in the morning. Five people may be still missing, Rader said.

“This is going to be all night into tomorrow,” he said, “we’re still going to be working on this.”

National Transportation Safety Board investigators are expected to arrive Friday to help determine the cause of the tragedy.

The boat, which had life jackets on board, capsized and sank due to intense winds and thunderstorms, Rader said. A severe thunderstorm warning was issued for the area at around 4:30 pm local time.

“The winds were behind what is called a ‘gust front,’” reported weather blogger meteorologist Mike Smith. “There were also intense winds with the heavy rain when it arrived which would have decreased visibility to very low values.”

Gusts of up to 70 or 80 mph were reported around the time of the sinking, he wrote.

The duck boat that sank was one of two still operating during the storm, Rader said. The boats were returning to shore when the incident happened, he said. Some of those on the stricken boat were able to swim to shore, the Kansas City Star reported.

Video captured by onlookers just before the incident showed two duck boats churning up and down through choppy waves, with water spraying in every direction.

One of the boats lags behind the other, nose-diving into the waves. A speed boat can be seen driving up behind the duck boats.

“Oh my gosh, oh no,” a woman is heard saying in the background of the video. “Somebody needs to help them.”

“That duck, I don’t know if they’re going to make it back,” a man is also heard saying on the video.

Another video was captured by a passenger inside the second duck boat, which made it safely to shore. Footage from Paul Lemus and published by local news outlets shows a number of adults and children inside the boat. Waves crash up against the windows and the Showboat Branson Belle can be seen docked nearby, on the lake’s shore by Table Rock State Park.

According to the Southern Stone County Fire Protection District, multiple agencies responded to the scene of a “mass casualty incident” involving a “tourist type boat,” shortly after 7 pm local time.

At 7:16 pm, a call to Taney County Public Safety dispatch asked for a “water rescue” just north of the site of the Showboat Branson Belle.

“Will be a duck that has capsized. We have approximately 30 individuals in the water,” said a voice on the dispatch, according to a recording captured on Broadcastify.com. “It’s pretty intense here,” another voice said later.

Among the boat’s passengers was a sheriff’s deputy, who immediately assisted in the rescue effort, according to Rader.

At 7:27 pm, a voice over the dispatch said several people had already “been picked up.”

“We have injuries, a possible CPR in progress. There’s a couple of pontoons to get people out of the water.

“Some people are already on land,” another caller said later. “We do definitely need an ambulance there.”

One responder asked if those at the scene of the victims could push back bystanders. “We have people out here taking pictures.”

Just before 7:45 pm, another member of the response team said they had “at least six or seven fatalities.”

“We’re trying to dive for more missing people,” he said. “We’re treating some, obviously the injured ones.”

The storm rolled in suddenly while Rachel Zerby was camping along the lake near where the duck boat capsized, she told The Washington Post.

“We have a clear line of sight to both across the water,” Zerby said. “I noticed most of the boats had left the water, but there were still at least two or maybe three ducks still near the Belle.”

Rader told reporters he did not know how deep the water was where the boat sank. He said he believed the deaths to be caused by drowning.

“This is a very tough night for us. It’s going to be a long night for a lot of people,” Melody Pettit, communications manager for the city of Branson, said during a press briefing outside city hall. “It’s gut-wrenching.”

Families of victims were welcomed to gather inside city hall overnight. The city set up a command post inside, offering chaplains, psychologists and Red Cross services to families, Pettit said.

Originally created by the US Army for use in the Second World War, DUKWs (called “ducks”) were amphibious trucks shaped like boats that ferried ammunition, supplies and equipment from offshore ships to troops stationed on beaches. In later years, they were modified for recreation and riding in duck boats has become a highly popular tourist activity.

The duck boat that capsized was owned by Ride the Ducks Branson, a tourism company that takes people on tours of the Ozarks through land and water using the amphibious vehicles. Ride the Ducks is a national company that has multiple locations across the US, including Guam. The Branson operation was purchased last year by Ripley Entertainment, a company spokesperson Suzanne Smagala-Potts told The Washington Post.

Duck boats have had a history of fatal accidents both in the water and on land.

In what may be the most deadly incident, 13 people died in 1999 after a duck boat suddenly started taking on water while on a tour of Lake Hamilton in Hot Springs, Arkansas.

In 2015, a Ride the Ducks boat crashed into a charter bus on the Aurora Bridge in Seattle and five college students were killed. Dozens of people were injured. Ride the Ducks International LLC agreed the following year to pay $1 million for violating federal safety regulations, according to the Seattle Times.

However, Smagala-Potts said this is the first time there has ever been an accident involving the duck boats in Branson. The company has been operating in the city for 40 years and is “a staple of Branson,” Smagala-Potts said.

“We are deeply saddened by the tragic accident that occurred this evening at Ride The Ducks Branson,” she said. “This incident has deeply affected all of us. We will continue to do all we can to assist the families who were involved and the authorities as they continue with the search and rescue.”

Located about 20 minutes from Branson, Table Rock Lake is a popular destination for “watercraft aficionados,” according to its website. The lake stretches across 45,000 surface acres and 800 miles of shoreline.

Roger Brallier, who is a duck boat captain for the same company, told The Post that all of the captains are “very close.”

“Were it not for grace of God, it could’ve been me on the boat,” he also said. “All of our hearts are completely broken right now.”