He was sleeping when his young grandson knocked on his bedroom door.
Mr Junid Salim, 70, opened the door and saw fire coming out of another bedroom.
After shouting for his grandson to run, Mr Junid grabbed two pails of water in quick succession to put out the fire. But the elderly man, who is a cancer patient, fell while carrying the third pail.
A neighbour persuaded him to leave the burning unit.
The fire, which happened yesterday evening, engulfed a bedroom in the ninth-storey flat at Block 699B, Hougang Street 52. It also left black smoke marks on the exterior walls of three units above it.
The Singapore Civil Defence Force (SCDF) received a call about the blaze at about 5.40pm. It sent two fire engines, one Red Rhino, two fire bikes, one support vehicle and one ambulance to the scene.
The blaze was extinguished within 10 minutes using two water jets, an SCDF spokesman said.
Two occupants had left the unit before SCDF arrived and no one was taken to the hospital, the spokesman added.
Recalling the incident, Mr Junid said he was at home with his five-year-old grandson at the time.
Mr Junid recounted: "He knocked on my room and when I opened the door, a large fire was already raging (in another room). So I went to the toilet, took a pail of water and used it to try to put out the fire. After that, I took another pail of water and did the same."
Meanwhile, he asked his grandson to run.
Mr Junid was carrying his third pail of water when he fell.
He recounted: "I was not very well. I couldn't stand properly, that was why I fell when carrying the third pail."
A neighbour then pleaded with him: "Uncle, get out, get out, the smoke is very thick and dark already."
So Mr Junid left the burning unit.
He said: "I wasn't scared. My only thought was to put out the fire. I didn't want the fire to spread. I didn't think of myself at that moment, whether I inhaled smoke or not."
Mr Junid said that he was sleeping in his room with the door closed as he did not want his grandson to disturb him. He just attended chemotherapy earlier.
He said: "Before this, my daughter was with me. Then she went out - I don't know where she went - and left the boy with me."
When The New Paper was at the scene at 7pm, Mr Junid was lying on a stretcher.
His grandson, who gave his name as Arfan, was visibly shaken. When asked if he was injured, he said: "Just a bit."
Mr Junid's wife, 65, who checked the unit after the fire, lamented: "Everything inside is gone - living room, kitchen, all gone. Even the wires are falling off."
Mr Junid, who had just retired as a dispatch rider for an insurance company, said: "The thing is even though I worked for an insurance company, I didn't buy any insurance."
Neighbours said they first spotted thick black smoke, followed by fire inside one of the bedrooms. A sudden explosion then shattered the bedroom window.
A crowd, which had gathered at the bottom of the next block to watch the unfolding drama, ran for cover, witnesses said.
One of them, who lives on the sixth storey of the adjacent block, said she saw the fire from her living room.
Mrs Teo Thiam Guan, a housewife in her 40s, added: "The fire was coming out from a small window. Then we saw the window explode. I could hear the explosion from my unit and it was loud."
Another witness, Madam Wong Hoong Mooi, 58, a part-time cleaner, said she heard people shouting, "Fire! Fire!".
"I thought people were fighting downstairs. Then I saw a lot of smoke. Suddenly, there was a loud explosion. Everyone ran. I was so scared I didn't dare to leave my home."
MP for Pasir Ris-Punggol Gan Thiam Poh, who visited the scene last night, said he is asking HDB to help with temporary accommodation for the affected residents. The town council will also mobilise workers to clean up the mess.
The cause of the fire is being investigated.