From today, Pfizer eligibility expanded to people aged 16 to 39 across Victoria's 55 vaccination hubs as supply ramps up courtesy of 175,000 doses imported from Poland.

Some young people were able to break through the congested system, like Camperdown's Tom Goodwin, 31, who received his first dose of Pfizer this morning.

"When it became available yesterday I booked it last night and got in," he said. "The website crashed a few times after the announcement but I ended up getting through.

"I was holding out for Pfizer seeing how I'm only 31 and the risks associated with AstraZeneca didn't sit comfortably with me.

"I have to wait six weeks between doses which is a shame, I think they've extended the period since the announcement.

"I actually got it because it was only three weeks and I was hoping to get it done and dusted and get fully vaccinated within 21 days but now they've actually extended it to six weeks."

READ MORE: Where to get a COVID-19 vaccine in south-west Victoria

Within minutes of bookings opening, the state website appeared to buckle.

Many young people reported receiving a "500 internal server error" after waiting in the queue to book their appointment, while others were told they were ineligible for the vaccine.

Those aged 18 to 39 who have already made a first dose AstraZeneca appointment will be given the option to instead receive the Pfizer jab from the end of today, while 16 to 17-year-olds will strictly receive the latter.

Port Fairy's Tess Dempsey, 19, booked in for AstraZeneca a few weeks ago but wasn't able to receive Pfizer on Wednesday morning.

"I actually booked it the other week and then I found out today that they'd released Pfizer for our age as well," she said. "But honestly I'd rather get AstraZeneca and risk any side effects than get sick from COVID-19.

"My family own restaurants and it's been a lot tougher on them than it has on me, it's really hard on small businesses, especially in small towns like Port Fairy that rely on tourists.

"It's definitely important to get vaccinated so we can reopen and get on with everything."

Some under-40s in Warrnambool reported to The Standard the process was slow but they had secured appointments within the fortnight, even after the website timed out.

Others reported having to go as far as Portland and Horsham with Warrnambool booking out by 8.30am.

Yesterday was a record day for vaccinations in Victoria, with 31,629 vaccines administered.

There were 25,000 vaccination bookings made by 9am this morning.

1.3 million people tried to call the hotline this morning and the booking system is receiving 50,000 hits per minute.

Victorian Health Minister Martin Foley said state clinics had seen "an absolutely extraordinary" number of bookings for vaccines, since the Pfizer vaccine opened to people aged 16 to 40.

"We've seen that system under substantial pressure, but we've seen a huge numbers of bookings being made," he said.

It came as Mr Foley warned the outbreak continued to be the worst among young people, with about half of the state's new COVID-19 cases aged under 30.

More than a third of the state's active COVID-19 cases are in people aged under 20, with 114 cases aged under 9 and 101 aged 10 to 19.

Mr Foley said it was fantastic to see so many people wanted to be part of the state's way out of the pandemic through the vaccination program

He urged people to maintain their patience as the state worked through the extraordinary level of interest.

Mr Foley said while it was heartening to see a reduction in new COVID-19 case numbers over the past few days, it was the trend that public health officials would base advice around.

There are 300,000 appointments available between now and September 17.

Victorian Education Minister James Merlino announced all Year 12 school students will be prioritised to receive their vaccination before sitting their final exams.

Minister Merlino said the aim was to get all children aged 12 and over vaccinated before the end of the year.

Victoria recorded 45 new locally-acquired COVID-19 cases on Wednesday; 36 cases were linked to known outbreaks, while the source of the remaining nine infections are under investigation.

28 cases were infectious in the community and not isolating.

It brings the total number of active cases in the state to 538.

COVID-19 response deputy secretary Kate Matson warned some people were waiting as long as eight days after developing symptoms to get a test.

Ms Matson said if Victoria could shorten that interval it would help the state get on top of the outbreak sooner.

She said even vaccinated people should get tested, as they could still pass the virus on to others.

Ms Matson said two new cases were from the Hobsons Bay area, while others were from Hume, Melton, Wyndham, the City of Maribyrnong, Moreland, Monash and Glen Eira.

She said other new cases were linked to the MyCentre childcare in Broadmeadows, the Shepparton and Royal Melbourne Hospital Outbreak, Hobsons Bay and Wyndham, Melbourne's central business district and North Melbourne, and Glenroy West Primary.

Ten new cases were household contacts of unlinked cases.

See all the exposure sites here.

We have removed our paywall from our stories about the coronavirus. This is a rapidly changing situation and we aim to make sure our readers are as informed as possible. If you would like to support our journalists you can subscribe here.