In an address to the nation, Taoiseach Micheal Martin said, if left unchecked the new strain could pose a very real threat to hospitals in Ireland.

"It spreads so aggressively throughout all age groups that we are likely to see infections at a rate that is far in excess of anything we have seen to date. It is that serious." he said.

COVID news live: 65 patients in hospital with Omicron as UK emergency meeting planned

The new rules will come into force on Sunday 19 December and will last until 30 January.

What are the new measures?

Restaurants and bars should close at 8pm, with no indoor events after this time.

Venues should run at reduced capacity - for indoor venues it is 50% of capacity, or 1,000 people (whichever is lower) and outdoor events should be limited to 50% or 5,000 people (whichever is lower).

For close contacts of a positive COVID-19 case, if they have received a booster more than one week ago they will have to restrict their movement for five days and take three antigen tests.

For people who have not been boosted, they will need to restrict their movement for 10 days. The Health Service Executive (HSE) will consider the best testing regime for this category.

All overseas arrivals have to take an antigen or PCR test depending on their vaccination status and all passengers arriving should be advised to conduct antigen testing on a daily basis for five consecutive days.

Wedding receptions can take place after 8pm but with a capacity limit of 100 guests.

'It is not the news I wanted to bring you'

The taoiseach said he understood the news would be a blow to many families and businesses.

"It is not the news I wanted to bring you and it is not the news you want to hear. We will be in a much better place in 2022," Mr Martin said.

"We just need to get to the other side of this Omicron wave as safely as possible."

"This Christmas, please be safe and look after each other."

He said living with the virus does not mean returning to a life before the pandemic, adding: "It means understanding the disease, monitoring it, making changes when it changes and doing whatever we need to do to product people's lives and livelihoods."

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Chief medical officer Dr Tony Holohan told a briefing on Friday that the Omicron variant makes up 35% of COVID-19 cases in the country.

Optimistic models predict 8,000 cases a day and between 650 and 1,000 people in hospital, but there are concerns that increased socialisation at Christmas would exacerbate infections.