When he saw three men crowding outside his neighbour's flat, he knew something was amiss.
Plumes of black smoke were also coming out from the unit at Hougang Street 11.
Yeo Dao Quan, 13, knew there was no time to lose.
"I ran home and told my mother about it. Then, we filled up pails with water for the adults," the Secondary 1 student told The New Paper.
Other neighbours helped as well, using the water to try to put out the fire until the Singapore Civil Defence Force (SCDF) arrived at the fifth-storey flat.
An SCDF spokesman said it was alerted at 3.30pm yesterday. An ambulance, a fire engine, two Red Rhinos and two fire bikes were sent to the scene.
A boy in his teens was taken to the Singapore General Hospital for smoke inhalation, the spokesman said.
The cause of the blaze is being investigated. TNP understands that a liquefied petroleum gas cylinder was placed in the middle of the living room.
Before the SCDF officers arrived, Dao Quan was busy filling up the pails with his mother's help.
His brother, Dao Ying, joined in 10 minutes later when he returned home and saw the commotion.
Still in his school uniform, the 11-year-old ran downstairs to inform the younger brother of the teenager who was trapped in the flat.
"I was chatting with him at the bus stop before coming home. That was how his mother found out about the fire too," Dao Ying explained.
He and his brother left the pails at the staircase landing because their mother did not want them going too close to the fire for fear of an explosion.
But Dao Quan told TNP that the thought of danger did not cross his mind.
When asked if he was scared, he shook his head shyly and said he acted instinctively.
"There was no time to worry," he said.
Other neighbours, like part-time student Wang Qing Fu, 24, helped to throw water into the flat using the buckets the boys had prepared.
Mr Wang, who lives in an adjacent unit to the one that was on fire, initially thought the smoke came from incense offerings. He realised it was a fire only when a pizza delivery man rang his doorbell a minute later and told him about it.
Mr Wang added that he saw a boy crouching by the door of his neighbour's flat, with a blanket draped over him.
"We could feel the heat while standing outside the unit, so we were hoping the water would help take away some of the heat," he said.
As the door was locked, the SCDF officers had to saw the grilles of the gate to rescue the teenager who looked distraught and was gasping for air, said Major Tay Zhi Wei, the commander of Sengkang Fire Station.
The fire was put out in five minutes.
Major Tay said the keys to the flat had been left on the dining table.
He said: "It is not surprising that (the teenager) did not see the keys. The smoke was very thick."
He added that the dining table had been shrouded by smoke.
The fire left the living room and kitchen charred. The teen's mother, who was seen at the void deck crying, declined to comment.
This article was first published on Oct 24, 2014. Get The New Paper for more stories.