The men, aged 43, 44 and 54, are fighting for their lives at the Royal Adelaide Hospital.
One of the injured men jumped into a pool after being burnt.
Seven people were taken to hospital after the fire, which started at 6.30am at the Comfort Hotel Adelaide Meridien in Melbourne Street, North Adelaide.
The other four guests have been discharged from hospital.
Flames can be seen coming from hotel windows in footage shot from the street, with witnesses saying screams rang out.
More than 100 terrified guests desperately tried to escape.
Many managed to get out themselves, but around 15 people, some stuck on balconies, had to be rescued from the building by Fire and Rescue crews, using ladders and cherry pickers.
Carli Leishman said she saw a hotel room engulfed in flames.
“As we were going down the stairs we actually could see the room that was on fire and you could hear them screaming, ‘help, help’,” she said.
A ladder came to the rescue of Isla Whitfield, 11, and her family.
They’d just helped a line of terrified guests who’d been crawling blindly through the darkness, unsure of where an exit was.
Darren Whitfield said he called out to help.
“I called out to them to crawl, make sure you stay low, and out of the smoke comes these people and they have soot all over their faces, all over their body,” he said.
Brandon Swain, who is a wheelchair user, had to use the lift to escape.
Some guests say despite smoke in their room, they didn’t hear a fire alarm.
“That was the most terrifying thing because, well, it would have taken us a while if we had been asleep to register (there was a fire),” guest Jan Shirtcliffe said.
Firefighters believe the fire was accidental, however police are continuing to treat the blaze as suspicious until a full investigation has been completed.
Chief Inspector Matt Nairn from South Australia Police said the fire in the three-level building could have hurt more people.
“There’s always the likelihood that you’ll end up with a lot more injury or death with a fire of that scale where there’s multiple occupancy,” he said.
Officers have towed a vehicle from the carpark of the hotel.
It’s understood it belongs to one of the people who was staying in the room where the fire began.
Guests have since been escorted back into the hotel, with staff working with police to help arrange alternate accommodation.