Passengers from countries that will officially go on the category two mandatory quarantine list from tomorrow have been arriving at Dublin Airport.

Anyone traveling from an additional 16 countries, including the US, France, Canada and Italy, will have to enter mandatory quarantine from Thursday.

Less than three weeks after it was set up, the Government's mandatory quarantine system has had to pause bookings as it ran out of hotel capacity.

The Department of Health said this was due to a problem with "walk-ins" or people who simply turn up rather than having booked online before departure.

The Government has said 300 additional rooms will become available next Monday.

Today, passengers arriving from France and the US told RTÉ News that were relieved to get to Ireland before tomorrow's mandatory quarantine requirement kicks in.

"It's my last chance before an unfair quarantine regime starts," one passenger said as he arrived from Paris.

"The whole thing is ridiculous, waste of time, too late and utterly pointless."

Another passenger who returned from the US said she felt a sense of panic when she learned the news.

"I was home for a funeral and to move my parents out of their house and into a retirement community.

"It's very scary to think that you could be stuck in mandatory quarantine and have to pay for it as well," she said.

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Social Democrats co-leader Róisín Shortall said the had "descended into chaos less than three weeks" after it was set up.

She said: "Given there are nearly 150,000 hotel rooms in Ireland, most of which are empty, it beggars belief the Government is unable to find additional capacity.

"Health Minister Stephen Donnelly has now said the system will be unable to accept bookings until Monday, when 300 additional rooms will become available.

"Given passengers from an additional 16 countries will be entering mandatory quarantine from tomorrow, can he give any guarantee that this paltry figure will be enough?

"Has the Government done any modelling to gauge the projected demand for these rooms?"

The Government has been criticised for not giving enough consideration to the damage that quarantining does to people's lives and to business.

"There's such a scale of investment in Ireland that people being cut off from their investments is a really dangerous place for them. Are the benefits worth the cost?" IBEC's Danny McCoy said.

Airlines 'breaking the law' if they allow boarding without certain documents

In relation to mandatory hotel quarantine, Minister Donnelly said airlines are breaking the law on public health grounds if they let people board the plane without the pre-flight PCR test, the passenger locator form and a verified hotel room.

Speaking on The Hard Shoulder on Newstalk, Minister Donnelly said capacity is not the issue with mandatory hotel quarantine, as Ireland has enough rooms to deal with people coming in where they have verification.

He said the problem is that a number of airlines have not been enforcing the legal requirements.

The number of rooms available will increase to about 960 on Monday, he said, and this will increase again to more than 1,300 the following Monday.

He said they are looking at a way for those who are fully vaccinated to be able to move to home quarantine rather than hotel quarantine.

"I don't apologise to anyone for putting in place measures that are designed to keep the people living in Ireland safe from variants of concern," Mr Donnelly said.