Gov. Charlie Baker. Photo by Chris Van Buskirk | State House News Service

Massachusetts will move into the third phase of its gradual plan to revive public activity in most of the state on Monday, allowing gyms, museums, movie theaters and more to resume some operations even as COVID cases surge in other parts of the country.

Phase 3 will last longer than the other phases, and Baker reiterated Thursday that the fourth and final section will not begin until treatment or a vaccine for COVID-19 is available.

The Baker administration’s decision shifts Massachusetts toward the leading edge of states on the path to reopening, pushing forward despite peers pumping the brakes on their own progress due to concerns about massive outbreaks in the south and west.

Citing positive trends in public health data, Gov. Charlie Baker said Thursday that he is confident the state can loosen restrictions without prompting an infection rebound because bars and nightclubs will remain closed and because residents and businesses continue to abide by safety precautions.

“The success is due in no small part to the vigilance and dedication that has been shown by the people of Massachusetts, but we should not and cannot slow down or step back now,” Baker said. “We know that COVID-19 won’t be taking any time off this summer, and we need to maintain vigilance if we wish to continue to move forward.”

Phase 3 will consist of two smaller steps, though administration officials have not yet announced when the second portion will start. The loosened restrictions in the first step will take effect in Boston on July 13, one week after every other community in Massachusetts.

Under the first step, movie theaters, museums, fitness centers and some indoor recreation facilities that have all been closed since mid-March will be allowed to reopen so long as they follow industry-specific protocols. Most will face capacity limits and mandatory cleaning requirements. Indoor and outdoor events such as weddings or parties will not be allowed to open bars or dance floors.

The administration will also update restrictions on gatherings to allow more people to congregate, starting July 6 statewide and July 13 in Boston.

Indoor gatherings will be capped at eight people per 1,000 square feet with a maximum of 25, while outdoor enclosed gatherings will be limited to 25 percent of permitted capacity with a maximum of 100. Caps do not apply to unenclosed outdoor events, such as backyard parties or park visits.

Baker said the next step along the path toward the new normal will bring back “some bigger players that will certainly draw more people into indoor settings,” where public health experts say the risk of COVID transmission is far greater than outdoors. That underlines the importance of individual caution, he said.

Professional sports teams will be permitted to host games without spectators in Massachusetts as part of Phase 3, though Baker said he is “not prepared to sign off” on any plans to bring fans back.

Business groups reacted to the announcement with mixed feelings, with the National Federation of Independent Business of Massachusetts saying the good news comes amid “many shops and restaurants closing their doors permanently.”

The right-leaning Massachusetts Fiscal Alliance, which has been one of Baker’s most vocal critics during the state of emergency, said the next stage of reopening “is the best gift Massachusetts taxpayers can give our country on its Birthday.”

“With over 100 days being locked down, and Phase 3 beginning on Monday, the Governor is finally putting his faith in the people of Massachusetts to make the best decisions for themselves,” MFA spokesman Paul Craney said in a press release. “Every day that goes by, it’s clearer that this lockdown is yesterday’s news and it should never happen again.”