(NEXSTAR) – Amid a nationwide baby formula shortage that has parents scrambling to feed their little ones, breast milk banks across the country are seeing a surge in interest.

The calls are coming in from both parents of formula-fed babies who suddenly can’t find their brand on shelves, as well as nursing mothers with excess supply who want to donate.

The Human Milk Banking Association of North America (HMBANA), an accrediting organization for nonprofit milk banks, is seeing a “major increase” in demand, according to Lindsay Groff, the group’s executive director. She estimates inquiries from parents seeking to fill the formula gap are up 20% in recent days.

Groff called the shortage a “crisis” and said it’s not as simple as parents just supplementing with donated human milk, because the vast majority of those supplies are earmarked for babies with medical conditions.

If you are interested in donating milk, the HMBANA has a curated list of vetted milk banks across the U.S. After going through a screening process, you can drop milk off in person or use overnight shipping at no cost, according to the Texas-based organization.

Milk banks in Texas, California, Colorado and other states have put out a call for donations in the past couple of months amid a shortage exacerbated by supply chain issues and formula recalls.

Dr. Lisa Stellwagen said San Diego-based University of California Health Milk Bank is focusing on helping babies with health problems whose mothers’ milk might be insufficient.

“It’s premature babies,” explained Dr. Lisa Stellwagen. “Babies with cardiac illness and other sick babies that would be typically given donor milk if mother’s milk was insufficient.”

“We’re really not talking about healthy, full term babies unless the family has an interest in feeding the baby donor milk,” she continued. “We’re talking about these really, very ill children.”

It’s not just donors reaching out to milk banks, though. Parents desperately seeking nutrition for their babies are pursuing milk banks as well.

At the Mothers’ Milk Bank Northeast, based in Newton, Massachusetts, people are now calling looking for milk because they can’t find their baby’s usual formula, Deborah Youngblood, the bank’s executive director said. That’s up from nearly no calls at all, since the milk bank typically serves hospitals.

Parents are also turning to online breastmilk-swapping forums to meet their babies’ needs.

Amanda Kastelein, a mother of three from Middlebury, Connecticut, has been supplementing the special formula she needs for 10-month-old Emerson with breast milk from a mom she found on a peer-to-peer Facebook page called Human Milk 4 Human Babies.

Kastelein stopped breastfeeding after getting recurring infections, but tried to begin re-lactating in March after the formula recall, with little success.

“Emerson is allergic to most of the formulas, so it’s been difficult to find something he’s not allergic to,” she said.

In stepped Hannah Breton of Naugatuck, Connecticut, who had been producing more milk than her 2 1/2-month-old son needs. She’s been giving Kastelein about 60 ounces of milk every two weeks. That’s enough to supplement her formula supply and keep Emerson fed.

“She asked a bunch of questions — what medications I’m taking, if any, that kind of thing,” Breton said. “So we decided, ‘OK, that’s perfect.’ So, she comes by every couple weeks and picks up the milk I’ve been saving for her.”

“I do feel helpful,” she added. “It’s exciting and rewarding that I can give to a mom that can’t find what she’s looking for, and if her son can’t take formula, I mean, it’s scary.

Rebecca Heinrich, director of the Mothers’ Milk Bank in Colorado, advises those looking for milk that searching for donors on their own can carry risks.

“We want to make sure that these moms are being as safe as they can and meeting the needs of their infant, so consulting with their health-care provider on how to meet those needs is the best way to go,” she said.

The shortage creates difficulties, particularly for lower-income families after the recall by formula maker Abbott, stemming from contamination concerns. The recall depleted many brands covered by WIC, a federal program like food stamps serving women, infants and children, though it now permits brand substitutes. Abbott says it has been working with WIC and the USDA to pay rebates for competitive products when Similac isn’t available, which is slated to continue through August 31.

Abbott said Monday it had reached an agreement with U.S. health regulators to restart production at its largest domestic factory, though it will be well over a month before any new products ship from the site to help alleviate the national shortage facing parents. A spokesperson for the company said that after FDA approval Abbott could restart the site within two weeks. New product would likely land on store shelves between six and eight weeks after the restart.

“Today’s action means that Abbott Nutrition has agreed to address certain issues that the agency identified at their infant formula production facility in Michigan,” FDA Commissioner Robert M. Califf, M.D. said in a statement Monday. “The public should rest assured that the agency will do everything possible to continue ensuring that infant and other specialty formulas produced by the company meet the FDA’s safety and quality standards, which American consumers have come to expect and deserve.”

Abbott did not immediately detail the terms of the agreement with the Food and Drug Administration, which has been investigating safety concerns at its Sturgis, Michigan, plant since early this year.

“After a thorough investigation by FDA, Centers for Disease Control and Prevention (CDC) and Abbott, and review of all available data, there is no conclusive evidence to link Abbott’s formula’s to these infant illnesses,” an Abbott spokesperson told Nexstar in an emailed statement.

The consent decree amounts to a legally binding agreement between the FDA and the company on steps needed to reopen the factory.

The Associated Press contributed to this report.