Doctors have been left "gobsmacked" after Alfie Evans' life-support was withdrawn but he continued to live, his father has said.
Tom Evans said it was obvious that the youngster was breathing unassisted "within a few minutes" of life-support being withdrawn on Monday night.
Mr Evans continued: "They say Alfie's suffering. Well look at him now. He's not even on a ventilator and he's not suffering."
Earlier, a High Court judge had dismissed a "last-ditch appeal" by Mr Evans and Alfie's mother, Kate James, to be given more time to mount a further challenge to a decision to end the 23-month-old's treatment.
Speaking outside Alder Hey Children's Hospital in Liverpool on Tuesday morning, his father said Alfie's life-support should be reinstated due to his remarkable progress.
"He is still working, he's doing as good as he can," he told reporters.
"But we do need him to be supported ... in the next hour it's going to be hard but we will need him to be supported in the next hour or two.
Alfie's parents want treatment to continue and want to fly him to a hospital in Rome.
His case has been highlighted by the Pope, who expressed support for the couple, and he has been granted Italian citizenship.
Mr Justice Hayden analysed issues at a hearing in the Family Division of the High Court late on Monday.
The judge heard submissions from lawyers representing hospital bosses, Alfie's parents and the youngster via a telephone link.
However, Mr Justice Hayden refused their application for more time and gave doctors the go-ahead to stop treatment and bring Alfie's life to an end.
After life-support was withdrawn, Alfie continued breathing and doctors agreed to give him oxygen and water, Mr Evans said.
"They say Alfie's suffering. Well, look at him now. He's not even on a ventilator and he's not suffering," he told reporters.
Mr Evans said that he had a "lengthy talk" with doctors and pleaded with them to give his son oxygen.
"They left him for six hours without food, water and oxygen," he said.
"He's now on oxygen. It's not changing his breathing but it's oxygenating his body."