By day, the area behind Safra Tampines seems typical of a cluster of industrial buildings.
The eight blocks of flatted factories at Tampines Industrial Park A comprise car workshops, furniture makers and warehouses.
Come nightfall, however, the place transforms into a secret dormitory for foreign workers.
Some 1,000 foreign workers sleep in these workshops and flatted factories, hidden behind partitions.
At night, streams of lorries unload workers at these illegal dormitories.
Some of the dorms are in units marked "under renovation".
One person who tipped off The New Paper thinks there are about 8,000 people sleeping in these eight blocks at night.
TNP spent two weeks staking out the place. Going by the number of buses ferrying in workers, there seemed to be about 1,000 workers staying there.
The flatted factories are owned and managed by the Housing Board (HDB) and the illegal dorms are clearly violating HDB's rules.
TNP understands that most of the offending units are owned by companies that house their own workers, while some units are leased out to other companies.
The workers seem to be from a number of construction, electrical and manufacturing companies, going by the registration details of lorries ferrying them in and out of the area.
We spoke to the director of one construction company which has a warehouse there.
Twelve foreign workers live in the back of the warehouse. The unit also has a kitchen area and washing facilities hidden from plain view.
Said the director, who did not want to be named: "Here (in this area), there's a lot (of other dormitories), too.
"Just come down on their Sunday rest day and you can see for yourself."
He claimed the workers all have dormitories outside, but they told him they prefer to stay there.
When told that it was illegal, he said: "Yes, I know. You don't understand the construction culture here.
"The costs for hiring a foreign worker are getting higher and we're not a big company. If there are no complaints, then why not?"
During our stake-out, we saw workers in sarongs and pyjamas gathered at staircase landings and the roadside, where the Wi-Fi signal is strongest.
There is even a system to ensure the workers are fed. At around 7am, they collect food from marked boxes at the foot of the block, left there by caterers.
Before 9pm, when they return from work, they collect dinner from these boxes.
At the more than 20 units that The New Paper managed to enter, we saw racks of laundry hanging from window panes and piles of shoes at the entrance.
People speaking in various languages could be heard from within.
The smell of curry was a dead giveaway that food was being prepared.
Each unit had two entrances, but one was almost always locked.
Most of the workers declined to speak to TNP.
One worker from India revealed that there were many workers' dormitories in the eight blocks, but he could not estimate exactly how many.
"I like living here better (than commercial dormitories)," he said.
"I have freedom - there's no curfew. I can cook whenever I like. I get (transport) to work, too."
He said he had no idea living there was illegal as it was provided to him by his boss.
Other workers who spoke to TNP appeared to have been told what to say.
"Oh, we're not staying here," said one Chinese national at a unit owned by a contractor.
"We're waiting for a pickup."
Another Indian national allowed us into the office area, but stopped us from going behind the partitions.
"No, no one is sleeping there," he said, despite the piles of shoes and slippers at the doorway of these "rooms".
What was he doing there past midnight? "I'm doing overtime," he replied.
And no, he had not heard about the fire at a Geylang shophouse that killed four foreign workers two weeks ago. That shophouse had been converted into living quarters for workers.
Since then, there has been a rash of illegal housing activities reported.
Employees of businesses operating during the day at Tampines Industrial Park A said they were not surprised to hear about the illegal dorms.
One tenant, whose warehouse is opposite an illegal dormitory, said foreign workers have been living there for a long time.
He declined to give his name, saying the tenants have a habit of "closing one eye".
He said: "I know about it. I can see them through my window, but if I say anything, I'll be condemned (by the neighbouring tenants)."
A security guard who has been working in the area for a decade said: "There are thousands of workers living in illegal dormitories here and no one knows about it."
He had contacted TNP to tip us off to the situation.
"This one has 12 workers. That one has 20," he said, pointing out unit after unit.
The living conditions are appalling, he said. Rats and mosquitoes are common, he claimed. The workers' activities also pose a significant safety risk.
"You see the cooking area? It's right next to the place where they make furniture," he said, pointing at a video he took of the interior.
He added: "The most I've seen in a unit is 40 people.
"When I give the list to the authorities, they will send people down to investigate . But these workers know how to disappear. They will return in a few days when the coast is clear."
Additional reporting by Ariffin Jamar.
This article was first published on December 27, 2014. Get The New Paper for more stories.