The Chief Medical Officer has said he was "absolutely shocked" by the crowds that gathered in parts of Dublin city centre on Saturday evening.

Dr Tony Holohan said the scenes in the South Great George's Street, Exchequer Street, and South William Street area were "like a major open air party".

On Twitter, Dr Holohan said: "This is what we do not need when we have made so much progress."

A statement tweeted by Dublin City Council said there was a significant amount of waste left behind overnight and added: "Gatherings of this size and nature are contrary to current public health regulations."

South William Street in Dublin being cleaned up today

Meanwhile, Chief Executive of the Health Service Executive Paul Reid acknowledged the sacrifices made by "young and old" and reminded people that there were still many risks with the virus.

The comments follow those of Taoiseach Micheál Martin, who on Friday said that continuing advances against the spread of infection required adherence to public health guidelines.

In a statement, gardaí said four people were arrested for public order offences.

They reminded people that the Covid-19 pandemic remains a public health crisis and said a policing operation was put in place following reports of a large number of people congregating at South William Street and adjoining streets.

The operation involved gardaí from the Public Order Unit and the Dog Unit and the crowd was subsequently dispersed.

People congregating in Temple Bar and St Stephen's Green were also dispersed by gardaí. No arrests were made.

Twelve people were also arrested for public order offences in Cork overnight following large crowds gathering at a number of locations in the city centre yesterday.

Uniformed gardaí, with the assistance of the Public Order Unit, dispersed large numbers of people who had gathered throughout the afternoon at Kennedy Quay, Grand Parade and Oliver Plunkett Street.

Gardaí appealed to the public to abide by the ongoing public health guidelines, not to gather in large groups, keep social distancing and wear face coverings in crowded public spaces.

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Clean-up under way at Cork's Kennedy Quay this morning

Meanwhile, public health doctors have warned the variant first discovered in India could soon become the dominant strain in Ireland if case numbers remain high.

Public health doctors say they fear the variant could jeopardise the gains made if cases of it increase. Fewer than 100 cases have so far been detected.

The Department of Health has been notified of 374 new cases of Covid-19. There are 99 people with the virus in hospital; 35 in ICU, which is unchanged from yesterday.

Additional reporting Jennie O'Sullivan