Dublin is experiencing another surge in Covid-19, acting chief medical officer Dr Ronan Glynn has warned.
He said he did not want to sound alarmist, but 73 of the 147 cases of the deadly virus diagnosed yesterday were in the capital.
It is being watched closely, he added.
There is particular concern that one in three of the new infections in the capital are due to community transmission so the source cannot be found.
This is higher than in the rest of the country, where the rate is around one in five.
The biggest concentration is in Dublin west, south-west and north-centre but the cases are spread across the capital. Asked if this meant Dublin was heading for a lockdown, he said this was not planned.
The hope is the restrictions announced nationwide last week will have an impact on cases, he added.
He also warned that more than 160 children under the age of 14, many of whom will be attending school, could be diagnosed with Covid-19 over this week and next.
Dr Glynn was speaking as the nation's classrooms nervously reopen for the new school year amid heightened concern about the risk posed to children and teachers from Covid-19.
He said cases of the virus have been rising among children and a total of 84 were diagnosed last week.
"Of course if nothing changes we can expect a similar number this week and next week.
"Many of those children will be in school, so it won't be a surprise if we have cases in school-aged children but the challenge for us in the first weeks is to respond appropriately."
Parents have been told if there are concerns for their child in a school they will be informed by public health team.
Dr Glynn said he hoped the spreading of misinformation and rumours that marked the early days of the virus here would not be repeated.
Meanwhile, cardiologists in hospitals across the country have treated a number of younger people who recovered from Covid-19 but have been left with heart-related complications.
Professor Robert Byrne, Director of cardiology services at the Mater Private Hospital in Dublin said the patients were found to have myocarditis, an inflammation of the heart muscle.
"We have seen it in patients under 40 years of age who had the virus," he revealed.
It is more evidence that some people who believe they have beaten the infection are left with a range of after effects, including cardiovascular damage.
Prof Byrne, who is chair of cardiovascular research at the Royal College of Surgeons, said there is a need to investigate further the impact of the virus on the heart.
"A small number of patients have developed myocarditis in the acute phase of Covid-19 illness. The symptoms can be a flu-like illness, followed by breathlessness and chest pain.
"The chest pain can be quite sharp and it can get worse when people take a deep breath in."
Cases are also being seen in other countries and a recent German study showed a group of people who were struck with Covid-19 had some degree of abnormality in their cardiac scans afterwards.
The study looked at people who recovered from the illness, most of whom were asymptomatic or had mild symptoms.
Two months afterwards almost 80pc had "persistent abnormalities", and 60pc had myocarditis.
"They seemed to be relatively young patients with a median age of 49 and a normal body mass index with relatively normal blood pressure."
Prof Byrne said although the study would need to be replicated the majority of cases here had no known coronary heart disease before being infected with the virus.
Prof Byrne said he is still very concerned that people who have heart disease, and were never infected with Covid-19, are still not seeking medical care because of their fears of catching the virus.
"It's a ticking time bomb," he warned.
"The hospital is still seeing around 20pc less new heart patients than it saw this time last year."