Massachusetts will see its first mobile COVID-19 vaccination clinics in communities hardest hit by the pandemic starting Monday, Gov. Charlie Baker announced Thursday.

"Most of these mobile units and pop-up clinics [will be] set up in city parks, parking lots and other places that are easy to access for community members," Baker said.

Baker spoke from a vaccination site in Chelsea, one of the communities that will host the mobile and temporary clinics backed by the federal government, along with Revere, Fall River, New Bedford and neighborhoods in Boston. Vaccines from federal supply lines will be distributed from the new mass vaccination facility run by the Federal Emergency Management Agency at the Hynes Convention Center in Boston.

Three days before Easter Sunday, and in the middle of Passover, Baker also warned residents to celebrate spring holidays only with their immediate family, saying that the virus can spread into another surge when friends and family don't take safety precautions, as happened during previous holidays in the fall and winter.

"We saw it happen at Thanksgiving. We saw it happen at Christmas. Let's try and make this particular weekend a little different than what we saw at the previous two," Baker said.

Asked why Massachusetts hasn't expanded eligibility for the vaccines as quickly or as broadly as some other states, Baker defended his strategy of balancing a focus on the oldest and sickest residents with greater access.

"Eligibility is one thing," Baker said. "Actually executing on the ground and getting big portions of the populations that are eligible vaccinated is another."

Every "significantly-sized state" that has been brought to Baker's attention for comparison has vaccinated fewer people per capita, has delivered fewer first doses and hasn't put their allotted vaccine supply to work as well as Massachusetts, the governor said.