At least 11 people, including children, died after an amphibious "duck boat” carrying tourists on a lake capsized and sank in stormy weather in the US state of Missouri Thursday night, the local sheriff said. Stone County Sheriff Doug Rader said five people remain missing and seven others were hospitalized after a Ride the Ducks boat sank on Table Rock Lake in Branson. Life jackets were on board the boat, he said. A spokeswoman for the Cox Medical Center Branson said four adults and three children arrived at the hospital shortly after the incident. Two adults were in critical condition and the others were treated for minor injuries, Brandei Clifton said. Rader said the stormy weather was believed to be the cause of the capsizing. Another duck boat on the lake was able to safely make it back to shore. Steve Lindenberg, a National Weather Service meteorologist in Springfield, Missouri, said the agency issued a severe thunderstorm warning for the Branson area Thursday evening. Lindenberg said winds reached speeds of more than 60 mph. Rader said an off-duty sheriffs deputy working security for the boat company helped rescue people after the accident. Video footage shot by an eyewitness who was on shore showed strong waves tossing two duck boats side to side. The video clip was posted online by KY3. Suzanne Smagala with Ripley Entertainment, which owns Ride the Ducks in Branson, said the company was assisting authorities with the rescue effort. Smagala added this was the Branson tours first accident in more than 40 years of operation. Branson is about 320 kilometers southeast of Kansas City and is a popular vacation spot for families and other tourists looking for entertainment ranging from theme parks to live music.