SAN FRANCISCO — In what is the largest single fundraiser ever on Facebook, a Silicon Valley couple has drummed up millions of dollars from tens of thousands of people to reunite immigrant parents with their children.

As of Tuesday morning, over 120,000 people had contributed more than $5 million to a Facebook fundraiser set up four days ago by Charlotte and Dave Willner and the pace is showing no signs of slowing.

The new target for the campaign, which started out at $1,500, is now $6 million. Right around the time on Monday night when the fundraiser sailed past $3 million, the couple calculated that $4,000 was rolling in every minute. Among those who have donated are Facebook's Mark Zuckerberg and Sheryl Sandberg.

"It's clearly resonating with a lot of people, and we're just glad we could help," Charlotte Willner told USA TODAY.

All of the proceeds from the Facebook campaign, "Reunite an immigrant parent with their child," benefit RAICES, a Texas nonprofit that provides free legal services to immigrants and refugees. Facebook, which launched fundraisers in 2017, waived fees last fall for nonprofit fundraisers.

Reached Monday night, Jenny Hixon of RAICES said: "This fundraiser has absolutely blown us away."

"Our fundraising infrastructure is spartan. We have one development person on staff, which is me...and I'm also responsible for overseeing our shelter, volunteer operations, media, community outreach, and refugee resettlement," she said. "We're very much a boots on the ground kind of organization."

RAICES will share its plans for the funds and let people know how they can get involved on Wednesday, said Hixon, who is the organization's director of outreach, education and development.

"We've rapidly reached out to other organizations doing complimentary work in Texas to set up a network to cover all the federal courts, develop a database with all separated families, and a pro bono referral network to ensure representation for every family," she said. "This feels outrageously ambitious, but we kind of feel like this is the moment to do the big things."

The Willners were early Facebook employees who now work at Pinterest and Airbnb. Overwhelmed by reports that nearly 2,000 children had been separated from their parents, Willner set up the fundraiser Saturday morning.

The initial goal was to raise $1,500 to cover the bond fees for one parent so they could retrieve their child from government custody while waiting for court. But then the fundraiser went viral and private donors began matching funds raised.

"Regardless of political party, so many of us are distraught over children being separated from their parents at the border," the Willners said in a statement. "We can’t all be on the frontlines to help these families, but by supporting RAICES, we’re able to do something that just takes less than a minute, and collectively have an impact.”

Late last week, the Department of Homeland Security announced that nearly 2,000 children had been separated from their parents in a six-week period as part of its "zero tolerance" policy. The Trump administration is cracking down on adult immigrants who cross the border illegally by criminally prosecuting them. Children can't be held in criminal detention, so they are being separated from their parents.

A 7-minute tape obtained by ProPublica, in which children separated from their parents and held at a detention center wail and call for "Mami" or "Papi" fueled the public outcryMonday.

Former first lady Laura Bush and America's other first ladies joined that outcry.

"Mrs. Trump hates to see children separated from their families and hopes both sides of the aisle can finally come together to achieve successful immigration reform," Melania Trump's communications director, Stephanie Grisham, told CNN Sunday. "She believes we need to be a country that follows all laws, but also a country that governs with heart."

Homeland Security Kirstjen Nielsen defended the Trump administration's policyMonday. "We have to do our job. We will not apologize for doing our job," she said. "This administration has a simple message — If you cross the border illegally, we will prosecute you."

Some of the comments on the Facebook fundraiser were supportive of the policy.

"Perhaps it's time for the parents of these innocent children (to) do the right thing by not putting themselves in this situation," wrote one person.

Hixon sees the situation very differently.

"The funding we are receiving will save lives. It will keep people from being deported to unsafe countries," she said. "It speaks to the outrage the cruel policies at the border have provoked. It honestly gives us hope in what has felt like a very dark time."