Two women and an infant were injured after a fire broke out on a yacht at ONE°15 Marina Club at Sentosa Cove yesterday.
One of the women is understood to be in serious condition, while the infant suffered injuries to the face.
The victims are in Singapore General Hospital (SGH).
Twelve other people, including some who had helped to put out the fire, were taken to SGH or National University Hospital with injuries from smoke inhalation.
A boat technician at the marina said he saw several people, including a woman carrying the baby, screaming as they ran from the burning yacht, which was berthed in a fuel dock.
Mr Derrick Sim, 33, and two colleagues from the boat maintenance team joined the club's emergency response team to fight the blaze before the Singapore Civil Defence Force (SCDF) arrived.
Mr Sim, who had cuts on the soles of his feet and was bathed in sweat, later said: "The yacht was badly burned. We could feel the heat from the flame from 150m away."
Witnesses said there was a bang, and the yacht appeared to be swallowed up in flames and black smoke in a matter of seconds.
Mr Shazan Ifham, who was working on board a nearby yacht, told The New Paper: "I saw black smoke and realised it was a fire. That is when I started to react."
The 27-year-old former firefighter, who is now chief skipper at a yacht charter company, said he called the SCDF, which arrived in about five minutes.
The SCDF said it was alerted to the fire at 4.30pm.
The club's emergency response team fought the blaze using hose reels before SCDF firefighters arrived and put it out with two water jets.
A club spokesman said the 15 victims included those on board the yacht and volunteer firefighters.
"The people on board the yacht evacuated shortly after the fire broke out. It was put out at about 4.50pm," the spokesman added.
It is not known how many people were on board when the yacht - identified by the club as Wilber - caught fire.
When reporters arrived at the scene at around 5.30pm, there were three fire engines, two rapid response fire vessels and more than 20 officers, including police officers and Sentosa rangers, at the dock.
The top half of the yacht had been destroyed, and there was the smell of petrol in the air.
Mr Sim said his feet were cut by glass shards from the yacht's melting windows after he had lent his slippers to someone else.
He said he did not seek treatment but that his two colleagues who had helped to fight the fire were taken to hospital for smoke inhalation.
Mr Brent Rubbo, who owns boat-dealing company Premium Nautical, said his boat, which was berthed near the burning yacht, was damaged by the heat from the flames.
The SCDF is investigating the cause of the fire.