The screams pierced the night, startling residents of the quiet Queens neighborhood of Flushing.

"I hear them from my bedroom window say, 'Help! Help! Help!'" said one neighbor.

Police said a worker at a day care center stabbed three babies, a co-worker and a man, and then slashed her own wrists.

Turns out, the business operating here was not a day care facility but a so-called maternity hotel, the Mei Bao, Mandarin for "beautiful baby."

The September attack opened a window into an unregulated, underground phenomenon — businesses caring for newborns and their mothers.

Some are Asian women already living in New York, but many are so-called "birth tourists" who travel to the U.S. just to have a baby so the child can automatically obtain American citizenship.

We found advertisements on Chinese-language websites for at least 36 of these maternity hotels in Queens alone, 33 of them just in the heavily Asian Immigrant community of Flushing.

Like the New York Yiya Confinement Center on Main Street; the An Kang Moon Center on 192nd Street; and on 161st Street, the Mei Bao - like many of the others, quietly operating in a residential neighborhood, without any signage marking its presence.

"A lot of them just function under the shadows, they just pop in random apartments or in random houses, so making it virtually impossible for the regulators and the enforcement agencies to even oversee them," said Assembly member Ron Kim, who represents the area.

But the hotels appear to operate with almost no oversight, benefitting from loopholes in state and city regulations governing child- and health-care facilities.

Because mothers are staying with their babies, the centers sidestep state classification as day care facilities.

And because they do not provide health care, the centers do not need a medical license.

The hotels are free to hire anyone, regardless of qualifications. Customers have no guarantees about the quality of care and usually no recourse when things go wrong.

"It's concerning that we have these maternity centers that seem to be for profit and seem to in some ways be taking advantage of women who are in a vulnerable position," said Dr. Andrew Ditchik, the associate director of Obstetrics and Gynecology at Elmhurst Hospital.

In an online forum, complaints about food in the hotels are common.

"Getting breakfast is like a competition. If you get up at 8, the only thing left there are two slices of bread," one forum post reads.

Hygiene is another issue.

"The nannies there feed the babies with the same bottle. As a result, several babies were infected with bacteria," one forum post reads.

But some approve of their experiences. One woman described the maternity center she used as "very professional, very clean, and the boss's attitude is very patient."

The city allows a business in a home, if it occupies no more than 25 percent of the space.

The law does forbid turning a home into a short-term hotel, defined as allowing stays of less than 30 days but an owner can get around that by living in the home, too.

"The only clear violation is potentially Department of Buildings violations, illegally converting rooms and occupancy rules. But as we know, when you call 311, Department of Buildings comes out, they may knock on the door a couple of times, can't gain access. There's nothing you can do about it," said Kim.

As for the Mei Bao, the victims all survived, and the arrested worker pleaded not guilty to four counts of attempted murder. The owner was not charged and is not under investigation.

According to Kim, the maternity hotel was back in business a short time later.

"Which was very concerning to me because there was clearly a tragic incident that occurred and how could a place possibly be reopened right away," said Kim.

The owner insisted to NY1 on the phone it is closed, and he "is no longer in the industry."

When we followed up with a visit, he avoided our camera. When we asked, "Are you still open for business?", he responded, "Stop talking!"