Singapore Civil Defence Force (SCDF) firefighters had to rescue a woman from a kitchen ledge after fire broke out in a fifth-floor unit of Block 158 Yung Loh Road at about 7.45pm on Sunday.
She and three others were taken to Singapore General Hospital and Ng Teng Fong General Hospital by ambulance.
A video by Twitter user Irsyad Syahmi shows thick plumes of smoke from the Jurong West Housing Board flat.
The woman was on the ledge for about 20 minutes, reported Chinese evening paper Lianhe Wanbao.
Residents had spotted her and notified firefighters who were then evacuating the building.
A couple and their two sons are said to live in the unit that caught fire.
SCDF is investigating the cause of the fire.