Since New York's first milk bank opened its doors in September, business has been thriving, with babies in need -- especially preemies -- receiving pasteurized donor milk via Fed Ex from a facility just north of Manhattan.

Now, for hospitals and mothers in a pinch, delivery can be door-to-door, thanks to members of New York City's oldest and largest female motorcycle club who can quickly transport breast milk throughout the city.

Known as the "milk riders," these women are on call at all hours, weaving in and out of traffic to deliver milk from the New York Milk Bank in Hastings-on-Hudson, N.Y., to babies at home or in hospitals.

"They are a fabulous group of women," Julie Bouchet-Horwitz, who founded the bank, told Fox News.

"We use them if we’re in a pinch and they're always able to help," she said.

"We will text the group that we need a run going from the facility into the Bronx," she said. "And sometimes it's late at night."

Bouchet-Horwitz, a nurse practitioner and lactation consultant, opened the bank in September and has since dispensed 30,000 ounces of milk to babies in New York and surrounding states, like Connecticut and New Jersey.

After the donated milk has been screened and pasteurized, it is typically packaged and sent to babies through the mail or delivered by a representative of the facility if the mother lives nearby.

Delivery to New York City, however, proved a challenge, especially for babies in urgent need of breast milk.

"I was stuck in traffic one day and saw a motorcycle weaving in and out," Bouchet-Horwitz told Fox News. "That's when I thought, 'Why can’t we use a motorcyle rider to deliver milk through Manhattan?'"

Bouchet-Horwitz then contacted the Sirens Women's Motorcycle Club, the city's oldest and largest women's motorcycle club founded in 1986.

The all-female crew was happy to help, according to Bouchet-Horwitz. The women, who also raised $2,500 for the bank, volunteer their time whenever a milk run is needed.

"They are volunteers and we pay their travel expenses," she said.

Bouchet-Horwitz recounted an incident in December in which a New York City hospital urgently needed milk for a mother who miscarried one of her babies while delivering twins.

"It was right around the holidays and the Hospital contacted us in a panic," the said. "And we had a rider ready and able to do a midnight run."

Pasteurized donated breast milk is critical for ill or premature babies whose mothers may not produce enough milk of their own.

The New York Milk Bank is the first of its kind in the state. Prior to its opening, New York relied on milk donations from states like Massachusetts and Ohio.

Bouchet-Horwitz said states that don't have milk banks, like Maryland, have expressed interest in her facility's services.

"We’ve had an unbelievable growth," she said. "Our freezers are filled with milk."