At least seventeen people, including nine members of one family, died when a tour boat sank during a storm in southern Missouri. (UPDATED)The Fargo Forum reports the duck boat capsized and sank Thursday, plunging passengers into a lake near the tourist city of Branson.

Authorities report that children were on board. The boat had 31 people on board, a crew of two and 29 passengers.

The office of Missouri Gov. Mike Parson reported Friday morning that the death toll had increased to 13 and the number of people still missing had declined to four. The governor also ordered flags in the state be flown at half-staff for a week.

Among the boat's surviving passengers was a sheriff's deputy, who reportedly assisted in the rescue effort.

Authorities said the boat sank because of intense wind and thunderstorms. The National Weather Service had issued a severe thunderstorm warning for the area.

Duck boat tours, which take place across the country, have resulted in fatal accidents in recent years.

[Source: Fargo Forum]