The first vaccination has been delivered after the SSE Arena in Belfast opened as a mass vaccination centre on Monday.
Up to 1,850 vaccines are due to be administered at the venue on Monday.
Centre vaccine manager Tanya Daly said seeing the centre in operation was "an amazing sight".
Up to 40,000 people could be vaccinated each week at the arena, where the AstraZeneca jab will be used.
Patricia Donnelly, the head of the vaccination programme in Northern Ireland, told BBC Newsline "it was like waiting for Christmas" and was a "momentous day for everyone concerned".
"We have got a very steady supply of AstraZeneca which is going to be used in this centre (SSE Arena) and also Pfizer which is used in other centres," she added.
"That steady supply has not let us down at any stage."
Ms Donnelly said that at the SSE Arena there was the capacity for 40,000 people to be vaccinated a week, but it would start with 10,000 a week.
"We build up over time, as we get more vaccine," she said.
A Covid-19 vaccination scheme at community pharmacies in Northern Ireland was also launched on Monday.
Health Minister Robin Swann said this would speed up the existing vaccination programme and ease access for people who may struggle to travel to a mass vaccination centre.
Speaking from the SSE Arena, where 16 vaccinators are working a 12-hour shift, Ms Daly told Radio Ulster's Evening Extra programme: "We are delighted that it is working so well.
"It's a fantastic team."
Ms Daly said the SSE Arena was not the clinical environment that staff were used to at the Ulster Hospital but that everything had been replicated to the same standards on a larger scale.
Stringent controls and procedures are in place and all staff have received rigorous theoretical and practical training, she said.
"We want people to have a good experience, but we want it to be safe," she said.
"We want to be sure that our vaccinators are not put under pressure; that the right questions are being asked and that everybody gets the vaccine that's appropriate."
Health officials plan to operate the vaccination service at the SSE Arena up to 14 hours a day, seven days a week.
Free car parking and shuttle bus services are being offered to people travelling to the arena for their jab.
Gary Davidson, 55, from east Belfast, received the first jab after 08:00 BST.
First Minister Arlene Foster said the opening of the centre was a "significant milestone" in the rollout of Northern Ireland's vaccination programme.
She said the number of people vaccinated would "rise significantly in the coming weeks".
Maggie Magowan, lead nurse at the South Eastern Trust vaccination centre, said it was a "monumental day".
"I would encourage everyone who is eligible to get booked in to help protect themselves, their families and our community," she said.
Chief executive of Community Pharmacy NI, Gerard Greene said pharmacies were "delighted to be playing their part" in the vaccination programme and their inclusion showed the "major progress" that is being made.
About 343 pharmacies in Northern Ireland are currently taking part.
In Northern Ireland, vaccines are available to people aged 50 or over.
Those who are eligible can book an appointment online, by phone on 0300 200 7813 or they may be contacted by their GP.
Exceptional times require exceptional responses and transforming one of Belfast's best-known entertainment venues into a mass vaccination centre in six weeks is one of them.
The achievement is down to the hard work and organisational skills of ordinary people.
Some people have likened fighting coronavirus to a war - once again we have seen a massive rallying of the troops in order to set up the vaccination of potentially thousands of people every day.
'Breaking the chain'
As the statistics demonstrate, vaccines are slowly breaking the chain from positive case to hospitalisation to severe disease and death.
And the opening of the SSE Arena offers a massive opportunity to step up the vaccination programme even further.
It also marks a significant step for the health service, allowing hospitals and GPs' surgeries to get back to what they should be doing.
At the same time, the Stormont executive has a challenge of Herculean proportions to keep the public on board - without a doubt there is significant feeling of emotional fatigue as a result of the pandemic.
Some good news on the horizon about the easing of some restrictions might just be the ticket.
The public transport options for travel to the SSE Arena include:
- Free shuttle bus service from the Europa Buscentre every 15 minutes from 07:45 BST to 20:15
- Free shuttle bus service from the Northside park-and-ride every 10 minutes from 07:40 to 20:20
- G2 Glider service operating every 15 minutes from the city centre
- Train service to Titanic Quarter station, a short walk from the arena
As of Monday, 730,471 people in Northern Ireland had received a first dose of a Covid-19 vaccine.
Some 125,017 people had received their second dose, meaning a total of 855,488 jabs have been administered in Northern Ireland.