TORONTO -- Ontario will expand vaccine eligibility to children as young as 12 as of Sunday, more than a week ahead of schedule.

The province had previously said that it planned to begin administering the Pfizer vaccine to children between the ages of 12 and 17 during the week of May 31 but in a news release issued late Friday afternoon it confirmed that it was moving that up to Sunday morning.

It said that it is making the change at “the request of some public health units to remove barriers for families requesting vaccines.”

Children could already receive vaccines at pop-up clinics and in select public health units, including Peel Region, but this marks a much wider expansion of eligibility.

It comes less than a week after Ontario began allowing all adult residents to book an appointment to receive a COVID-19 vaccine.

“We've worked with Premier Ford and the Province to open up eligibility in the booking system for young people 12 and up. This change will mean that anyone 12 and older can register to get vaccinated in our City-run clinics," Mayor John Tory said in a press release.

"We want everyone to get vaccinated, including our younger residents, so they can be safe and protected from this terrible virus. The sooner we are all vaccinated, the sooner this pandemic will be over. So please, if you and your family are not vaccinated yet book an appointment as soon as possible."

The city said SickKids will lead its youth vaccination efforts.

As recently as last weekend, those booking appointments through the provincial booking platform had to be at least 40-years-old or fall under another priority group.

But vaccine supply has quickly ramped up with Ontario expecting to receive a total of 4.3 million doses this month alone.

That, in turn, has allowed the province to accelerate its rollout.

So far the Pfizer vaccine is the only one that has been approved for use in children.

As of 8 a.m. on Sunday, children who are at least 12 years old can book an appointment to recieve a vaccine through the provincial booking platform or select pharmacies that offer the Pfizer vaccine.

More than 7.7 million doses of COVID-19 vaccine have already been administered in Ontario and about 59 per cent of adults have received at least one shot.