Updated 3:45 p.m.

COVID-19 vaccines will be available to all Massachusetts residents over 16 years of age by April 19, Gov. Charlie Baker announced Wednesday as he fleshed out the state's plan to distribute a large anticipated increase in vaccine supplies over the coming months.

Starting March 22, eligibility will open to residents 60 years old and older, as well as certain high-risk workers. On April 5, residents 55 and older will become eligible, along with residents with one medical condition that makes them at higher risk for complications from the virus.

"These dates are when we plan to make these groups eligible. It could take several weeks for the vaccine to get to Massachusetts so that everybody can get an appointment. And that will, at the end of the day, all depend on the availability of federal supply," Baker said at a press conference in Brockton.

The state's new preregistration system will automatically alert residents who are signed up when they can book an appointment at one of the state's mass vaccination centers.

Rep. William Driscoll Jr., D - Norfolk, who co-chairs the House COVID Oversight Committee, told GBH News that the new timeline is a positive step toward giving the public anticipatory guidance on their eligibility.

"They now understand when they're going to be eligible," he said. "The next [question] is when will I be invited to make an appointment, and when will I actually get the dose or the two doses," Driscoll said.

Driscoll hopes the Baker administration has a plan to keep in touch with those in the preregistration system over the weeks or months it will take to deliver each vaccine.

"If they're getting the same generic email for three months while they wait, I think that that's not going to curb the anxiety issues long term," Driscoll said.

Baker also announced a federally-funded $27.4 million program to enhance vaccine distribution in "priority populations" within the 20 communities hit hardest by the virus.

The funds will help pay for appointment registration assistance, transportation to clinics and interpretation services through the state's network of community health centers, behavioral health providers and community based organizations.

"The funding will be used to increase trust, vaccine acceptance and administration rates as part of the administration's vaccine equity initiative and to meet the needs of high risk populations," said Health and Human Services Secretary Marylou Sudders.

The state's “Trust the Facts. Get the Vax" program is also in line for federal funds to help its mission of disseminating information about the effectiveness and safety of the vaccine in communities hit hardest, such as Boston, Brockton, Chelsea, Fall River, Holyoke, Lawrence and Revere.

Though Baker is preparing for big increases in supply through April, the state will receive only a modest increase in its supply of first doses from the federal government this week, amounting to a total of 170,000 shots. Baker said he thinks the state is "going to see hundreds of thousands of doses" coming from the feds throughout April.

Baker said there will be three factors that the system uses to determine when appointments will be made available through the preregistration system: eligibility, when you entered the preregistration system and availability at your closest mass vaccination site.

The announcement drew a mix of fresh praise and criticism for Baker’s rollout procedure.

“This is important, helpful news, and I look forward to seeing regional sites added to the state registration system soon,” tweeted Mayor Tom Bernard of North Adams, one of Massachusetts’ northwestern most cities.

Currently, the closest mass vaccination site is a nearly two-hour drive from North Adams. The city does have two smaller vaccination sites at St. Elizabeth’s of Hungary Church and a local Stop and Shop store.

Advocacy Groups like the Vaccine Equity Now! Coalition responded by saying that proof of equitable distribution will be seen in the details.

“We need assurance that the 20%t additional allocation of doses promised in the administration’s original plan is now available to the hardest hit communities — something that we did not hear in this announcement,” said the group’s three co-chairs in a joint statement after news of the announcement spread.

Last month, the group issued five demands of Baker to ensure vaccine equity, including making vaccination goals that mirror the virus’ disproportionate impact on Black and Latino residents.

“We also want to hear that the administration has set benchmarks to track their own progress and hold themselves accountable to close these gaps,” the group said.

This week, mass vaccination sites like Fenway Park, Gillette Stadium and the Reggie Lewis Center in Roxbury received 101,890 first doses, and health care providers received nearly 100,000 doses. Community Health centers received 27,450. Local boards of health received 19,210, and regional collaboratives received 59,580 first doses.

Federal authorities also distributed another 106,440 doses to CVS Health sites through the federal pharmacy program.