Nine of the tourists who died in a duck boat accident in the US were from the same family.

The tourist town of Branson in Missouri was in mourning on Friday for sightseers killed when the boat capsized and sank in stormy weather in the deadliest such accident in almost two decades.

Divers found four more bodies in Table Rock Lake, bringing the death toll to 17, including nine people from the same family and the crew member who was driving the amphibious boat.

In their initial assessment, authorities blamed thunderstorms and winds that approached hurricane strength.

“Branson is a city full of smiles,” Mayor Karen Best said. “We have so much fun here. But today we are grieving and crying.”

Missouri Boat Accident Duck Boats
A duck boat sits idle in the car park of Ride the Ducks (Charlie Riedel/AP)

Trisha Ayers was among the mourners who stopped to pay their respects at a parked car that was covered with flowers because it was believed to belong to a dead tourist.

Ms Ayers said she understood how the boat got caught on the lake because the weather on Thursday changed in 10 minutes from sunshine to gale-force winds that bent traffic signs.

“I hope it won’t tarnish Branson,” she said with tears in her eyes. “About 80% of our income comes from tourists. We love them.”

The risk of heavy weather was apparent hours before the boat left shore.

The weather service station in Springfield, about 40 miles north of Branson, issued a severe thunderstorm watch for its immediate area pn Thursday, saying conditions were ripe for winds of 70mph.

It followed up at 6.32pm with a severe thunderstorm warning for three counties that included Branson and the lake. The warning mentioned both locations. The boat went down about 40 minutes later, shortly after 7pm.

“When we issue a warning, it means take action,” meteorologist Kelsey Angle said.

Missouri Boat Accident
Rina Bernard, left, and Keri Johnson leave flowers on a car believed to belong to a victim (Charles Riedel/AP)

Suzanne Smagala, from Ripley Entertainment, which owns Ride the Ducks in Branson, said the company was assisting authorities. She said this was the company’s only accident in more than 40 years of operation.

The boat was carrying 29 passengers and two crew members on a pleasure cruise, and everyone aboard had been accounted for by midday on Friday.

Seven of the 14 survivors were hurt when the vessel went down. At least two were in a critical condition in hospital. The captain survived, authorities said.

The mayor identified the crew member driving the boat as Bob Williams, known informally as “Captain Bob”.

“He was at a great ambassador for Branson,” Ms Best said. “He was at every event. He knew everyone. He was always promoting Branson.”

Authorities have not publicly identified the dead but said they included a one-year-old child.

Named for their ability to travel on land and in water, duck boats have been involved in other serious accidents in the past, including the deaths of more than 40 people since 1999.

Five college students were killed in 2015 in Seattle when a duck boat collided with a bus. Thirteen people died in 1999 when a boat sank near Hot Springs, Arkansas.

Missouri Boat Accident
Emergency workers patrol an area near where a duck boat capsized (Charlie Riedel/AP)

“Duck boats are death traps,” said Andrew Duffy, an attorney whose Philadelphia law firm handled litigation related to two fatal duck boat accidents there. “They’re not fit for water or land because they are half car and half boat.”

Safety advocates have sought improvements and complained that too many agencies regulate the boats with varying safety requirements.

The boats were originally designed for the military, specifically to transport troops and supplies in World War Two. They were later modified for use as sightseeing vehicles.

Passengers on a nearby boat described the chaos on the lake as the winds picked up and the water turned rough.

“Debris was flying everywhere,” Allison Lester said in an interview on Friday with ABC’s Good Morning America.