Some people aged 35 to 39 will now be able to access a Covid-19 vaccine in the North.
The region's Department of Health announced “limited availability” for that age cohort ahead of the vaccine programme being fully opened to them at the end of April.
People were able to book from 2pm on Monday, with appointments mainly available at the mass vaccine centre at the SSE Arena in Belfast.
The department said appointments in community pharmacies will be made available to 35-39-year-olds later in April as vaccine supplies permit.
Northern Ireland hit the one million Covid-19 vaccine mark earlier this month.
Health Minister Robin Swann said the vaccination programme in the region will proceed as quickly as vaccine deliveries and capacity allow.
“Opening up to 35-39-year-olds earlier than expected is a testament to the hard work and dedication of all staff who are delivering the vaccination programme in Northern Ireland,” he said.
“I encourage those who are eligible to seize this opportunity and take up the offer of vaccination.
“Getting the vaccine not only protects you but also those close to you.
“I would also strongly encourage anyone aged 40 years or over who hasn’t booked themselves a vaccination appointment yet to do so as soon as possible.”
Speaking in the Assembly on Monday, First Minister Arlene Foster hailed the latest development in the vaccine programme.
“Those people who are in that age group can now avail of the Covid vaccine and I would very much encourage them to make sure that they take that up,” she told MLAs.
The move comes as the North prepares to take further steps out of lockdown.
Last week, Ms Foster and Deputy First Minister Michelle O’Neill announced three key relaxation dates, April 23rd, April 30th and May 24th.
Under the plans, hairdressers can reopen on April 23rd, pubs and cafes can serve people outdoors from April 30th and indoors from May 24th.
Hotels will be able to fully reopen on May 24th as well.
Ms Foster said economic recovery “must now be very much our number one focus”.
“We know that there are industries and businesses right across Northern Ireland who have been in a really dire situation over this past year,” she told MLAs.
“We have tried to help through mitigations and through grants but we totally understand that the best way to recover is to be open and to be able to continue with business.”
On Monday, there were no further deaths of patients who previously tested positive for Covid-19 announced in Northern Ireland.
However another 79 people had tested positive for the virus, while there were 69 confirmed Covid-19 inpatients in hospital, eight of whom were in intensive care.