SINGAPORE - When Mr Xu Ming Lin's wife told him she smelt smoke, he rushed down to the seventh storey of their block and found two children playing on an iPad outside a four-room unit that was billowing black smoke.

Another concerned neighbour, Mr Damien Lim, 22, also hurried down to investigate.

Both men helped the family of the burning unit at Block 340A Sembawang Close evacuate safely.

On Wednesday, around 100 residents at the block also had to be evacuated because of the fire, which broke out at around 5pm.

Mr Xu, who lives on the 13th storey, said his wife had smelt smoke while having dinner with his parents at their unit on the ninth story.

The 28-year-old construction manager said the children looked to be around seven and 10 years old, and recalled asking them if they needed help and if there was a fire inside, but they did not respond.

Mr Xu, who was an SCDF officer during national service, said: "I knew something was wrong because there was so much smoke and the smell was so strong. I asked again urgently, hoping they would answer me so I could somehow help them."

He then quickly ran upstairs to his flat, where he kept a fire extinguisher. While he was rushing back to the seventh storey, he called the SCDF.

Mr Xu was about to break the extinguisher's seal when the SCDF arrived and told residents to evacuate by stairs. He also evacuated his family and shouted "Fire, fire!" to alert his neighbours.

Mr Lim, who had run down from his eighth storey unit, said: "When I reached the unit, I waited for a minute before a woman appeared at the door screaming for help."

The full-time national serviceman helped the woman and her three children to the stairs before returning to his unit to help his grandmother evacuate.

Another resident, who wanted to be known only as Mrs Chan, said she was at work when a neighbour called her about the fire. She immediately called her husband, who was home with their two teenage children.

She said: "My husband said the smell of smoke was very pungent and they evacuated the flat.

"I can't imagine what the neighbours on the eighth and ninth storeys are feeling, and the extent of damage to their homes after the fire."

Mrs Chan said her unit was filled with soot, with burn marks on her ceiling. The family cleaned up their home from 7pm to 1am.

On Thursday morning, a couple was seen entering the burnt unit to survey the damage.

When approached by The Straits Times about the cause of the fire, the woman said she believed it started from the electrical switches in the flat.

The man then pulled her away and they refused to answer further questions.

Three children were taken to hospital for smoke inhalation.

Sembawang GRC MP Lim Wee Kiak said on Thursday they have received donations of household items for the affected family, including a sofa set, a washing machine and clothes.

The SCDF and police on Thursday said the cause of the fire was under investigation.