Dr Holohan has repeatedly warned again people abandoning social distancing restrictions because of the danger of transmission of the Covid-19 virus.
He took to Twitter to express his shock and horror at scenes of revelry on streets in the South City Centre.
He stated: “Drove into Dublin City Centre to collect someone from work at 815 PM.
“Absolutely shocked at scenes in South Great George’s St, Exchequer St, South William St area.
“Enormous crowds - like a major open air party. This is what we do not need when we have made so much progress.”
Some of the streets where Dr Holohan witnessed the crowd scenes have been well-known in the past for large numbers of people congregating and drinking openly.
His expressions of alarm come at a time when there is deepening concern about the likelihood of the more contagious Indian variant of the virus spreading further within Ireland.
Gardaí also continued to urge people to follow the public health guidelines.
They said in a statement: "As public health regulations continue to be reduced and activity begins to normalise An Garda Síochána continues to remind the public of the ongoing public health guidelines, which include not to gather in large groups, maintain social distancing and wearing of face coverings in crowded public spaces. An Garda Síochána continues to appeal to the public to avoid crowded areas and large gatherings.
"The Health Act 1947 (Section 31A (6A)) (COVID-19) (NO.2) Regulations 2021 (SI 217/2021) are currently in force. Gardaí in Pearse Street are conducting high visibility patrols in Dublin city centre this evening.
"In supporting the COVID-19 public health guidelines and regulations, An Garda Síochána has and will continue to adopt, a graduated policing response based on its tradition of policing by consent. This has seen Gardaí engage, educate, encourage and, only as a last resort, enforce.
"The COVID-19 Pandemic remains a public health crisis and An Garda Síochána continues to appeal to all citizens to demonstrate personal and social responsibility to comply with Public Health Guidelines and Regulations, in order to continue to save lives.”
This latest controversy about crowd behaviour has happened as a further 464 confirmed cases of Covid-19 have been notified in Ireland.
The latest figures also reveal there are 90 Covid-positive patients in hospital, of whom 35 are in intensive care.
Taoiseach Micheal Martin said that while the end of the pandemic is “within our grasp”, he urged the public to “remain vigilant against the terrible virus”.