Appointment capacity for next week, which jumps by about 3000 across the AIS and Canberra Airport hubs, was accidentally used for bookings made this week, Heath Minister Rachel Stephen-Smith told ABC.

Next week will see a ramping up of "overall capacity between AIS and the airport, from about 20,000-21,000 this week to 24,000 next week," she said.

"But unfortunately, the capacity had been included, as if it was next week, for this week."

People waiting for appointments up to 5.30-6pm were able to get in and get vaccinated, the health minister said.

But people with appointments from 6.30pm were asked not to attend, and had their appointments rescheduled.

There were just over 600 appointments rescheduled.

However, due to the demand, staff had been "enthusiastically drawing up a lot of vaccines to ensure that they could get through all the additional people who are coming through the door," Ms Stephen-Smith said.

"And when those appointments were cancelled they actually ended up with a bit of excess supply having been drawn down into syringes ... so at that point, the team on the ground activated their wastage policy."

People were then contacted to come into AIS to receive the excess vaccines.

Ms Stephen-Smith did not say whether any doses were wasted as as a result of the chaos.

Extra staff were brought in to help with the backlog of people, with a system glitch blamed for the error.

It came after the ACT government opened up 30,000 extra bookings at its government-run clinics last week.

Long queues formed outside on Monday afternoon but many decided to rebook their appointments.

An ACT Health spokeswoman confirmed the delays were due to extra bookings.

"The extended waits are due to an error which resulted in overbooking beyond today's capacity," the spokeswoman said.

"Canberra Health Services increased staffing [on Monday] afternoon and our nurses are working as quickly as possible to get as many people vaccinated as they can."

However, not every appointment was able to go ahead. People were told they would be contacted to have their appointments rescheduled.

"While there is sufficient vaccine supply on hand, unfortunately not every appointment will be able to go ahead," the ACT government spokeswoman said.

"We apologise for the inconvenience and thank everyone for their patience. Anyone booked in [on Monday] who does not receive their vaccine will be contacted and offered a priority appointment in the coming days."

Kyle Gallacher was one of those waiting in line on Monday afternoon. His appointment was scheduled for 4pm, however, he was told to expect a two- to three-hour wait time.

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Mr Gallacher estimated the line was about 1500 metres long at about 5pm and about 750 to 1000 people were there.

He said there was little organisation and very few were prepared for the conditions as it started to get colder and darker on Monday evening.

The extra 30,000 appointments at the ACT government clinics came after extra Pfizer supplies were received from the Commonwealth.

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