Boston will move back to phase two of its reopening Wednesday forcing the closures of many indoor activities amid a drastic spike in COVID-19 infections, Mayor Martin J. Walsh announced Monday. 

The city had been in step one of phrase three of reopening since July 6. The new restrictions bring the closure of indoor spaces that had previously reopened, including movie theaters, gyms, museums, and indoor event spaces like meeting rooms. Somerville, Brockton, and Newton joined Boston in rolling back their reopenings. More cities are expected to join in the coming days, a press release from the Mayor’s office announcing the rollback said. 

The rest of Massachusetts remains in step one of phase three after Massachusetts Gov. Charlie Baker rolled back the state’s reopening from step two of phase three on Tuesday, which lowered maximum capacity levels from 50 percent to 40 percent for many indoor activities and reduced the cap on attendance at outdoor gatherings. 

Walsh’s decision comes amid a dramatic escalation of COVID-19 infections in Massachusetts and nationwide. The U.S. surpassed 300,000 COVID-19 deaths on Monday. Massachusetts averaged more than 4,000 daily cases over the past week, surpassing previous high case counts notched in mid-April. 

“Unfortunately, we are at the point where we need to take stronger action to control COVID-19 in Boston, and urgently, to ensure our health care workers have the capacity to care for everyone in need,” Walsh said in a statement. “We are hopeful that by reducing opportunities for transmission throughout the region, we will reduce the spread of this deadly virus and maintain our ability to keep critical services open.”

Initial shipments of COVID-19 vaccines began rolling out around the country Monday. The state plans to distribute 300,000 doses of the vaccine to health care workers and residents who face the greatest risk from the virus over the course of the next three months, Baker said last week. Each vaccine recipient will need two doses to reach 95% effectiveness. Boston Medical Center received 1,950 doses Monday while other area hospitals anticipate deliveries in the coming days.