OAKLAND -- Eight people working at a Habitat for Humanity site where former President Jimmy Carter will tour next week were robbed at gunpoint Tuesday afternoon, and one man was shot at and hit in the head with a pistol, police said.

Habitat staff members and AmeriCorps workers were robbed of their cellphones, wallets and other personal property at 1:40 p.m. Tuesday at the Brookfield Court development in the 9500 block of Edes Avenue in East Oakland, police said.

The man who was pistol-whipped was not hit by gunfire and refused medical attention. No one else was physically injured, police said.

Four men walked onto the property and robbed the seven men and one woman, ages 23 to 68, police said. Roughly a dozen other people were also working on the development, where 12 townhomes are under construction, but they were not robbed, said Habitat spokeswoman Krysta Morgenthaler.

The robbers drove away in two cars and police have not yet released full descriptions of the men or their cars. No arrests have been made.

"Everyone is a little shook up," said Morgenthaler. "Our primary concern is for our staff and team members who were there. It's unfortunate. We build in East Oakland, and we've been here a long time." She said the incident was a first at a Habitat site.

The robbery came just days before Carter and former first lady Rosalynn Carter are scheduled to visit Oakland and San Jose as part of a weeklong campaign highlighting Habitat for Humanity home-building projects. Joining them will be country singers Garth Brooks and Trisha Yearwood.

"We all do this (Habitat) job because we believe in the mission and the Carters believe in the mission, and (they) have made an investment in these projects," Morgenthaler said. "It is terrible what happened, but we are all determined to finish this project and continue to invest in the community."

A security guard is usually posted at the site starting at 5 p.m., but Morgenthaler said the guard is now there round-the-clock. A construction fence gate is also locked at all times, and police have stepped up patrols in the area, she said. The Secret Service and Oakland police are working together to gear up for the Carters' visit on Monday.

"The primary objective is keeping the Carters safe," said Morgenthaler.

Morgenthaler said everyone who was robbed was given crisis counseling Wednesday and the option to take the day off, but some have already returned to work.

Volunteer teams have spent months building 12 two-story townhomes at what was a vacant Edes Avenue lot. The future homeowners, who also helped in the construction, are expected to move in when the homes are completed by next spring.

The development is the latest of more than 100 new homes the nonprofit organization has built in Brookfield Village and the adjacent Sobrante Park neighborhood over the past decade.

Jimmy and Rosalynn Carter's involvement with Habitat for Humanity International began in 1984 when the former president led a work group to New York City to help renovate a six-story building for 19 families in need of decent, affordable shelter. The couple now visits Habitat sites during one week every year. Police and Crime Stoppers are offering up to $25,000 in reward money for information leading to an arrest. Anyone with information should call police at 510-238-3326 or a tip line at 510-773-2508

Staff writer Matt O'Brien contributed to this story.