The Stanford Blood Center announced a “concerning” blood shortage today, calling on South Bay residents to give blood as donations wane.

As of Monday, the center had only two to three days’ supply of certain blood types left, according to the center. Blood types O and A are in especially high demand.

“It really only takes a couple of heavier usage situations — a couple of people with more intensive surgeries — before we’re really in a scary place,” spokesperson Jenn Bennett told this news organization.

She added that through its call for donations, the center is working to be “proactive” about ensuring adequate blood supply before reaching that point.

The blood shortage has been partially driven by higher usage. The center carried out six transplant surgeries and multiple cardiac operations over the past week.

The supply also has been heavily impacted by the temporary closure of the center’s South Bay donor location in Campbell, which has been undergoing plumbing renovations since early June and is slated to reopen in August.

The Campbell location, located at 295 E. Hamilton Avenue, is “by far the most productive center” and usually brings in 15 to 25 percent of the center’s total blood supply, Bennett said.

According to the press release, Stanford Blood Center typically receives fewer donations over the summer months because many regular donors are traveling and schools — which hold blood drives during the school year — are not in session.

“Summer is historically a more challenging time for collections due to travel and busy schedules, so we’re asking folks to continue supporting local patients by donating at one of our other convenient locations,” said Renee Gipson, the center’s donor services director.

The center currently operates more than 60 mobile blood drives throughout the Bay Area, in addition to donor centers in Palo Alto, Menlo Park, Dublin, and Mountain View.

Interested donors can find a donation site near them and make an appointment online on the Stanford Blood Center website.