Donna Wood, an Australian passenger, said: "We saw smoke, we saw fire and my husband and I said 'I think we better jump into the river', and we did. We're Australian, we can swim."
Londoner Elissa Wood, who was on the tour with her parents, who were visiting from Australia, said the first they knew of the fire was when they noticed smoke pouring from the front of the craft.
She said: "We saw the tour guide and the captain look at each other like 'this is a real problem' and then they encouraged us to put life jackets on and jump off. It was really hot. The flames were really hot and it was confusing. We weren't sure what was happening so it was scary."
While all of the passengers and crew were quickly accounted for, the emergency services admitted the incident could have easily had tragic consequences.
London Fire Brigade station manager Simon Tuhill said most of those on board were visitors to the UK, with some coming from Holland, Sweden, Brazil and Australia.
"They were pretty pragmatic about it all," Mr Tuhill said.
"Obviously it was pretty scary for them. It isn't every day you sink in a boat in the Thames."
The boat is one of a number of amphibious vessels belonging to the London Duck Tours company, which offers pleasure cruises along the Thames.
Similar tours operate in other parts of the country and the Queen and Duke of Edinburgh took a trip on one last year during a trip to Liverpool.
But the refurbished craft, which are the same style as those used to ferry troops during the D-Day landings, have been beset with problems in recent months.
In June, 31 people had to be rescued from Albert Dock on the River Mersey when a duck boat got into difficulties and sank.
In July the Marine and Coastguard Agency grounded seven out of nine of the boats operated by London Duck Tours over safety concerns.
The company has been running tourist services on the River Thames since 2002, carrying more than 200,000 passengers.
The fire ravaged vessel was towed away from the scene by the London Fire Brigade and the Port of London Authority announced it would be holding an investigation into the incident.