A Tokyo hospital on Monday became the Japanese capital's first medical institution to offer a system allowing the safe, anonymous drop-off of infants by parents unable to raise them.
Used for centuries globally, so-called baby boxes or baby hatches are meant to prevent child abandonment or abuse.
But they have been criticized for violating a child's right to know their parents, and are also sometimes described by anti-abortion activists as a solution for desperate mothers.
Newborns within four weeks of age can now be placed in a basket in a quiet room with a discreet entrance at a hospital in Tokyo run by the Christian foundation Sanikukai, AFP reported.
The scheme, open 24 hours a day, is meant to be an "emergency, last-resort measure" to save babies' lives, Hitoshi Kato, head of Sanikukai Hospital, told a news conference.
There are still "mothers and babies with nowhere to go", the hospital said in a statement, citing the "abandonment of infants in baggage lockers, parks or beaches".
Sanikukai is only Japan's second medical institution to open a baby hatch, after the Catholic-run Jikei hospital in southwestern Japan's Kumamoto region opened one in 2007.
At Sanikukai in Tokyo, when a baby is put in the basket, a motion sensor immediately alerts hospital staffers to the drop-off, sending them rushing downstairs to tend to the baby, project leader Hiroshi Oe told AFP.
After confirming the baby's safety, the hospital will work with authorities to help decide the "best possible" next step, including foster care or a children's home.
If the person leaving the baby is seen lingering around the hospital, efforts will be made to engage them, Oe said.