The Chinese newspaper, Lianhe Wanbao, reports that the real target of the fire, however, might be the flat below the two units.
According to the newspaper, the alleged debtor who lived in the lower flat was the guarantor for a friend who has apparently defaulted on his loan.
The Police said they were informed of the fire around midnight.
The two families were reported to have been sleeping while the fire was raging outside their doors.
They only became aware of it when the Singapore Civil Defence Force (SCDF) officers woke them by knocking on their doors.
The police is reported to have installed a closed-circuit camera outside the alleged debtor’s flat on the 11th floor of block 272, Toh Guan Road, following earlier police reports by the family of being harassed by loan sharks.
The camera had apparently deterred the loan sharks who chose to target the two flats below the debtor’s.
Madam Chen, one of the victims, told Lianhe Wanbao that she was asleep with her husband and son when the fire occurred.
"We completely had no idea what was happening. We got a shock when the doorbell suddenly rang in the middle of the night," she said.
"We are innocent and got implicated for no reason,” she added. “Setting fire outside our homes can lead to fatalities.”
Another of the victims, who only wants to be known as Ms Liu, said, "We were awakened by the firemen who rang our door, and when we came out of our bedrooms, we found the whole house filled with smoke.
"The floor near the front door was covered with black oil," she added. "We were told to immediately evacuate when we went outside."
"After the incident, the father of the person targeted by the loan sharks came to me to apologise, saying the debts were owed by a friend of his son, and that his son was only the guarantor," said Ms Chen, one of the affected residents.
"The father offered to re-paint our door, but since it was badly burnt, I turned him down," she told the Chinese paper.
No one was reported hurt in the incident, and the SCDF said the fires were put out by the time they arrived on the scene.
A neighbour told the Chinese paper that the doors of the debtor’s flat was opened when the loan sharks were loitering outside it earlier that day, and this was why they did not set fire to the house then.
Police are investigating the incident and have classified it as "suspected unlicensed moneylending harassment by fire".
In January this year, four male youths aged between 15 and were arrested for their suspected involvement in a series of loan shark harassment cases involving fire.
They were believed to have set fire to items such as slippers, newspapers and cloth, placed at the front of residential units. (See here.)
This was similar to another incident a year earlier, where another group of four youths was arrested for involvement in “a series of island-wide loan shark harassment involving setting of fire and locking of gates.” (See here.)
In August 2013, a loan shark runner “committed more than 100 harassment offences in a month”, the TODAY newspaper reported.
These included “setting fire to the doors of HDB flats and locking the gates from the outside.”
The judge in that case of 26-year old Rinto Abd Rahim described it as one of the “most horrific” cases she had come across.
Mr Rinto was fined $60,000 and sentenced to almost 6 years in jail.
He was also ordered to be caned 24 strokes.