More people are renting out their homes for short periods, despite the growing awareness that it is illegal.
The Housing Board investigated 184 cases of short-term leasing in public flats last year, a 73 per cent increase from 106 cases the year before.
It also received around 45 complaints about suspected cases from 2012 to last year.
Violators may lose their flats and get fined if they are found guilty of renting out spaces for less than six months.
Private home owners are not exempt from the six-month rule. They can be fined up to $200,000 and be jailed up to 12 months.
The authorities say that such short-term rentals are banned as they might disturb neighbours in residential estates.
An Urban Redevelopment Authority (URA) spokesman added that most residents prefer "familiarity" and not to live among "transient strangers".
But that has not stopped more online advertisements offering these short-term rentals, which span a few days to months, from sprouting.
Roomorama's co-founder Teo Jia En, 32, told The Straits Times that her home-rental portal has more than 500 listings for Singapore properties, an increase of about 30 per cent compared to last year.
Mr Turochas Fuad, 39, chief executive and co-founder of travelmob, a similar website, also noted an "increased adoption of hosts and listings" across Asia Pacific, though he declined to provide numbers for Singapore.
A search on travelmob turned up over 500 local listings, and another portal, Airbnb, has more than 1,000.
Many of these listings are for short-term rentals, and most appear to be of condominium units and rooms.
The URA looked into about 2,100 unauthorised uses of private residences last year, up from 1,300 cases in 2011.
These numbers include both short-term leases and unauthorised conversions of private properties into dormitories or boarding houses.
But owners and tenants, many of whom sublet their homes to help pay their mortgage or rent and to meet new people, said that they have not received any complaints from neighbours.
"They are very supportive," said a 40-year-old business owner who has been renting out a room in her Novena condominium on Airbnb since June 2012.
She has had 13 bookings so far, with guests, usually tourists, paying $110 each night and staying for three days on average.
"It's such an incredible opportunity to meet people from all over the world without leaving your living room," said a 29-year-old marketing manager who started subletting the master bedroom in her four-room Chinatown HDB flat last December.
Apart from tourists, some of her guests are students or those here on work attachments who stay for weeks.
Visitors prefer renting these spaces rather than staying at hotels as they are often cheaper and include access to amenities such as a kitchen.
For example, one can rent a room in a Chinatown flat for $35 a night or $230 a week, while a hotel room in the same area might cost about $150 a night.
Ms Teo said: "It allows them to live like locals, which is unlike what they would get in a cookie-cutter hotel."
While Mr Fuad said that most travelmob guests prefer to stay in the central area for convenience, Ms Teo noted that Roomorama's most popular rentals are in East Coast and Bukit Timah.
"They prefer a respite from the hustle and bustle of the city centre," she explained.
Asked whether they help to enforce the short-term rental rules, Mr Fuad replied: "We do state in our terms and conditions for our hosts to understand their local laws before they list on our site."
"The onus is on the home owners to make sure they are in compliance," added Ms Teo, noting that licensed serviced apartments advertise on her website.