NEW YORK -- Yankee Stadium was opened as a COVID-19 mass vaccination site Friday by officials trying to boost inoculation rates in surrounding Bronx neighborhoods hit hard by the pandemic.

The home of the New York Yankees is being restricted to residents of the New York City borough with the highest percentage of positive coronavirus test results. Mayor Bill de Blasio called it "a different kind of opening day" hours after a long line formed outside the stadium on a damp morning.

"This is about protecting people who need the most protection because the Bronx is one of the places that bore the brunt of this crisis of the coronavirus" he said at a stadium-side news conference. "The Bronx has suffered."

De Blasio, a Red Sox fan, donned a Yankees cap in gratitude to the team and declared himself a fan of Boston's archrival "for one day only."

The site established with help from the city and state has registered about 13,000 of the 15,000 appointments available in its first week, officials said. It will initially be open seven days a week, 8 a.m. to 8 p.m. Officials encouraging people to get vaccinated enlisted former Yankees star relief pitcher Mariano Rivera to help. The Hall of Famer said he wanted to support the people who supported him for so many years.

"We saved so many games here," Rivera said, "but now it's about saving lives."