Greg Hunt says vulnerable children will be given priority access to Pfizer vaccines, with a further decision on all children expected soon.

Expert approval of the vaccination of all children aged 12 to 15 for COVID-19 could be given within weeks.

The timeline was revealed on Monday as approval was given for children as young as 12 who have impaired immune systems or come from other vulnerable groups to get priority access to Pfizer vaccines.

The jabs are approved for children aged between 12 and 15 if they are immunocompromised, have an underlying medical condition, are Indigenous or in remote communities.

Federal Health Minister Greg Hunt said this meant about 220,000 children would be able to get a Pfizer vaccine.

The rollout officially begins on August 9, but GPs are free to start administering vaccines to eligible children before then.

While the Therapeutic Goods Administration last month approved Pfizer for children in that age group, Australia's expert panel on immunisation had to give the final nod.

"They identified that there was a significantly greater risk for those immunocompromised or with underlying medical conditions," Mr Hunt told reporters in Canberra.

The minister also revealed authorities were reviewing international evidence with regards to all children from 12 to 15, with a decision on approval expected within six weeks.

"They will do an assessment looking at international data with an expectation that over the period in late August to possibly early September ... they'll come back with advice on the general population," Mr Hunt said.

"The early indications were that they were leaning towards that decision (to approve)."

The conditions covered by the initial advice for children include severe asthma, obesity, diabetes, cardiac and circulatory congenital abnormalities, neural developmental disorders, epilepsy and compromised immunity.