Student Pierce Ng was watching YouTube videos on the sofa when he heard a loud bang, followed by people screaming, yesterday morning.
Assuming that it was a case of domestic disturbance, the 17-year-old ignored it and continued watching videos in his seventh-storey flat at Block 235 Toa Payoh Lorong 8.
Pierce, who is waiting for his O-level results, said he "didn't think too much of it".
"But when my helper went out, she saw a very big fire," he told The New Paper.
Stepping out of his flat, Pierce saw the fire that had engulfed the unit on the sixth storey, with thick grey smoke billowing up.
Together with his father and their domestic helper, he rushed to the scene with bottles and pails filled with water.
They tried to put out the fire by splashing buckets of water.
Pierce said he also called the Singapore Civil Defence Force (SCDF) immediately.
An SCDF spokesman told The New Paper that officers responded to the incident at 8.52am and that the fire had broken out in the living room.
Another resident, Mr Ricarte Vicente, 42, an embalmer, said he saw the windows shatter.
Pierce said someone helped another resident living in the flat next door to escape.
The SCDF finally extinguished the fire with a water jet.
No one was at home at the time of the incident, and the SCDF confirmed there was no reported injury. The cause of the fire is still under investigation.