The number of coronavirus cases in Dublin could double every 14 days, public health chiefs have said.
And household and extended family transmission of the virus has been pinpointed.
Three further people have died from Covid-19 in Ireland, the Department of Health said.
Statement from the National Public Health Emergency Team— Department of Health (@roinnslainte) September 9, 2020
The Health Protection Surveillance Centre @hpscireland has today been informed that 3 people with #COVID19 have died.
There has now been a total of 1,781 #COVID19 related deaths in Ireland.
Acting chief medical officer Dr Ronan Glynn said: “People are letting their guard down in social settings.”
The rate at which the infection is spreading in Dublin is estimated at about 1.4, epidemiologist Professor Philip Nolan said.
“If nothing changes, if we do not act now to reduce our contacts and to be much more careful in how we manage our essential contacts the number of cases in Dublin would double every 14 days,” he added.
“There is a very clear call to action here.”
Prof Nolan pinpointed the march of the disease in the capital to social interaction in and between households and extended families.
Transmission is diffuse across the county, is in all age groups and is mainly being driven by social interaction within and between householdsDr Ronan Glynn, acting chief medical officer
The statistics show that older people are continuing to limit their encounters, the public health team said.
Dr Glynn said: “We continue to see a concerning pattern of cases, particularly in Dublin.
“Transmission is diffuse across the county, is in all age groups and is mainly being driven by social interaction within and between households.”
Data suggested more older people were being infected because the disease was spreading more widely.
Prof Nolan said that in the past 14 days there had been 89 cases recorded in people aged over 75.
He added: “That is close to a trebling compared with the preceding fortnight.”
Across the country, another 84 cases had been confirmed, the National Public Health Emergency Team said.
Close to 70,000 tests were being carried out per week.
Dr Colm Henry, chief clinical officer at the HSE, said: “The greatest risk of transmission to schoolchildren is in the home setting.
“International experience reveals that reopening of schools has not been associated with significantly increasing community transmission.
“Instead, it is transmission of virus within communities that poses the greatest threat to schools.
“Again, we urge all households to think through their social plans.”