Thirty people were rescued when an amphibious tourist vessel on the River Thames caught fire close to the Houses of Parliament.
Many people jumped into the river from the London Duck Tours craft.
All the passengers and crew were rescued by the emergency services and a passing tourist boat.
Those rescued were mainly "wet and cold", said London Ambulance. Some people had suffered the effects of inhaling smoke.
Three people were taken to hospital "as a precaution" said an ambulance service spokeswoman.
Those on board are believed to have included visitors from the UK, Brazil, Russia, Australia and Sweden.
About "five or six" young children were believed to be among the passengers.
Passenger Donna Wood said she jumped from the craft.
"I was scared the boat might blow. It was scary.
"There was a lot of smoke inhalation, so we jumped in the water.
"We're Australian, so we know how to swim. But I've lost my bag with my passport, everything I need to get back to Australia."
London Fire Brigade station manager Simon Tuhill said: "Our crews worked really hard to extinguish that fire and get the people out of the water.
"There were 30 people on the boat and most of them ended up in the water.
"They were suffering from being too cold and wet.
"Fortunately it was low tide so they weren't in very deep water."
A Scotland Yard spokesman said: "Several Metropolitan Police units attended, including the Marine Policing Unit and the police helicopter.
"A number of people were recovered from the water.
"All 28 passengers and two crew members have been accounted for."
The damaged boat was pulled away from the scene and the fire service has begun an investigation into how the fire started.
The Port of London Authority is also expected to investigate the blaze.
John Bigos, managing director of London Duck Tours, said he had no comment to make at present.
The Duck Tours website states: "No river cruise in London gives you the excitement of leaving the road and entering the Thames in such dramatic fashion and no River Thames boat cruise is as quirky as a London Duck Tour."
An operating licence for amphibious vehicles in Liverpool was revoked last month, after two vessels sank in the city's Albert Dock.
A number of tourists were rescued during the sinkings in March and June.
The Yellow Duckmarines were a popular attraction, offering tours of Liverpool.
The Queen and the Duke of Edinburgh travelled on one of the converted World War II craft during the Diamond Jubilee tour last year.