What the Seattle mayor’s office is calling the largest civilian-run vaccination site in the country opened Saturday at Lumen Field Event Center and administered 2,160 doses.

The event center, located between Seattle’s two pro sports stadiums downtown, will initially vaccinate about 5,000 people a week, but that could stretch to 150,000 — if supply is available, according to Mayor Jenny Durkan’s office.

Appointments remain available for the next mass vaccination clinic, scheduled for Tuesday afternoon, said Kelsey Nyland, who leads communications and outreach for the city’s vaccine effort. The mass vaccination site is operated in partnership with First & Goal, which owns the facility, and Swedish Health Services.

The first day’s clinic was “smooth” and “joyful,” Nyland said, with no long lines and people moving quickly through the space — which housed an emergency field hospital, albeit unused, in the early weeks of the pandemic.

The city plans to administer 1,200 doses at the site on Tuesday to people who live or work in King County and are in phases 1A, 1B Tier 1 and 2.

Another clinic is planned on Saturday, with an expected 3,100 doses, Nyland said. Information on how to join an email list to be notified of available appointments at Lumen Field Event Center and other city operated sites is available at www.seattle.gov/vaccine.  People can also call (206) 684-2489 for help scheduling, Monday through Saturday from 8 a.m. to 5 p.m.

Looking ahead, the site will be open two to three days a week, likely on Wednesdays and Saturdays.

Last year, Army soldiers set up a 250-bed field hospital at the site, but it shut down without being used when Washington’s projected COVID-19 cases were lower than expected.