Gillette Stadium has been home to a near-undefeated football season, two outdoor hockey games, a Major League Soccer final, many dozens of concerts, and next week, it will host another landmark event: the first mass vaccination site in Massachusetts.

In six days, Gillette will open its doors to hundreds of first responders per day who can receive Covid-19 vaccinations, then continue to scale up capacity to serve more people as they become eligible, Gov. Baker announced Tuesday.

After touring the Worcester Senior Center that started vaccinating first responders on Monday, Baker said the stadium will become the first of several locations to host large-scale immunization efforts in the state.

“These vaccines are safe and effective, and millions of doctors, nurses, and health care workers are getting vaccinated across our country,” Baker said. “This is a huge step forward in our fight.”

Massachusetts started making vaccines available to police, firefighters, EMTs, and other emergency personnel on Monday at more than 100 local sites and individual departments.

The Worcester Senior Center alone surpassed its initial capacity and hosted 376 vaccinations on Monday, Baker said, citing an “overwhelmingly positive response from first responders to get vaccinated.”

When Baker unveiled a plan last week to vaccinate the more than 45,000 first responders in the state, he said mass vaccination sites would serve as a key pillar to support the effort and then expand to other populations.

Tuesday’s announcement puts a clear timeline on the start of that segment: On Thursday, staff who will administer the vaccinations will receive their own vaccines, and then Gillette will open to first responders next Monday. Those eligible can schedule appointments at mass.gov/covidvaccine.

CIC Health will operate the site, while Brigham and Women’s Hospital will serve as medical director and Fallon Ambulance will support clinical staff.

“Gillette plans to start out doing 300 vaccines per day, but is going to build up to administering 5,000 vaccines per day and potentially much bigger numbers than that over time,” Baker said.

Baker also announced that his administration “in the coming days” will press forward into the next step of vaccine rollout, which will make doses available in congregate care settings such as correctional facilities and shelters. He promised more information “later this week.”

That step would take Massachusetts into the fourth population group of six included in the opening stage of the vaccine rollout, leaving only home-based health care workers and health care workers doing non-COVID-related care remaining on the Phase One list.

The original plan Baker and his administration outlined in December anticipated the second phase, with four targeted subgroups prioritized, starting in February, then the vaccine becoming available to the general public in April.

Through Thursday, Massachusetts had administered about 140,000 first doses of the vaccine and received about 328,000. That data is published once a week.

“I said back in December that I expected that the early part of this rollout would be bumpy, and it’s more than lived up to my expectations with regard to that,” Baker said on Tuesday. “But that’s partly because there was a lot of debate and discussion about how long the manufacturing process would take to ramp up, how the distribution model would work with respect to both the vaccines that would be delivered directly to providers.”

Baker urged federal leaders to provide states with clearer information about vaccine distribution so they can plan more efficiently, citing challenges that come with only having a few days of projections.

“We don’t have 20 or 30 days’ worth of visibility into what the distribution plan looks like, so it’s very hard for us to make predictions about where we’re going to be a month from now,” he said. “If we’re only hearing what our next dose is going to look like two days from now, the farthest I’m willing to go out is a few days. I think it’s critically important for us not to overpromise on this stuff.”

The Trump administration is preparing new guidelines that will recommend expanding vaccine eligibility to adults older than 65 and distributing additional doses as quickly as possible, according to an Axios report on Tuesday.

Baker, who last week bumped up the priority level for Massachusetts residents 75 and older, said he would consult a group of medical experts who have advised the state’s vaccination plan on the potential new guidance.

Governors were scheduled to speak with Vice President Mike Pence in the afternoon Tuesday about the Covid response. Asked about the prospect of pressing Pence to trigger the 25th Amendment and remove President Donald Trump from office after last week’s riot in the Capitol, Baker replied that he intended to focus on vaccine rollout.

“I’m pretty sure most of that dialogue is going to be about the vaccination rollout program and a big push on our part to get more visibility into this so that we can plan on a more forward-looking basis and put more shots in people’s arms when vaccines become available,” the governor said.