Facebook CEO Mark Zuckerberg and his wife, Priscilla Chan, are donating $5 million toward construction of a new health center in East Palo Alto.

The announcement was made Wednesday on behalf of the couple during a ground-breaking ceremony for the Ravenswood Family Health Center. Zuckerberg and Chan were unable to attend.

Zuckerberg and Chan are the most recent donors among many Silicon Valley dignitaries, businesses and organizations that have contributed to the $29 million project. So far, $21.6 million has been raised to fund the construction.

The 38,000-square-foot facility will house all health services except for administration. The Zuckerberg/Chan donation will cover the final costs for building the facility. Another $7 million is needed for equipment and furnishing after the construction is completed.

Construction could begin in a month, pending approval of permits by the city, Ravenswood Health Center CEO Luisa Buada said. The center is expected to open in spring 2015.

Since 2001, Ravenswood has provided comprehensive medical, dental and mental health services in East Palo Alto out of portable buildings at 1798-A Bay Road in the city's industrial zone, surrounded by car repair and sheet-metal shops. About 97 percent of the health center's clients are ethnic minorities and 93 percent live at or below the poverty line, East Palo Alto Mayor Laura Martinez said. Of its 150-member staff, 45 percent are hired from the community, making the center one of the largest employers of East Palo Alto residents in the city.

The new facility will double Ravenswood's service capacity from 11,000 to 22,000 patients per year. It will have 58 exam rooms, 13 behavioral health counseling rooms and will include a laboratory, imaging and mammography capabilities, optometry exams and pharmacy services.

The center will also support the expansion of residency programs in pediatrics, internal medicine and family practice, Buada said.

The announcement and ground-breaking was met with cheers and applause in a white tent at the new site, which is located at 1885 Bay Road near Pulgas Avenue. The location is across the street and about a block south of the current center.

The new facility is a far cry from the days when pediatric vaccinations were conducted from the back of a pickup truck, said Chris Dawes, president and CEO of Lucile Packard Children's Hospital and a member of Ravenswood's advisory council.

Dawes became involved in helping develop the original Ravenswood Center after helping a Packard Hospital pediatric fellow's project to vaccinate East Palo Alto children in 1998. He and the student drove around to apartments and offered the vaccinations from the back of the truck.

"It made me a bit nervous. I thought, 'There's got to be a better way to do this,'" he recalled. He joined a blue-ribbon task force to create Ravenswood. CEO Luisa Buada had initially planned to stay on as a consultant for three months, but she stayed on to build the Belle Haven Clinic in East Menlo Park, the Center for Health Promotion, which offers classes and programs for clients with chronic illnesses, and Ravenswood Family Dentistry.

"Are you tingling? This is so exciting for each and every one of us," Congresswoman Jackie Speier, (D-San Mateo), said.

The center received $5 million for construction from the Health Resources and Services Administration, which got the money through the Affordable Care Act, she said.

Congresswoman Anna Eshoo (D-Palo Alto), who has long been involved in supporting Ravenswood, hailed the project as a long-needed community resource.

"This has been the most underserved community in our region and we all knew it, and something had to be done about it," she said.

Major donors include the David & Lucile Packard Foundation, Palo Alto Medical Foundation/Sutter Health, Silicon Valley Community Foundation, John and Sue Sobrato and the Sobrato Family Foundation, John and Jill Freidenrich, Dick and Sue Levy, and Gordon Russell and Tina McAdoo.