© Tom Honan/PAMicheal Martin
Taoiseach Micheál Martin issued the warning as he said there was rising concern over the increasing rate of Covid-19 detections in major urban centres in Cork, Limerick, Waterford and Galway.
Dublin is already subjected to a three week lockdown in a bid to slash virus numbers.
The entire county of Donegal has also been subjected to a three week lockdown after virus case numbers soared.
Mr Martin said the Government will now consider city-wide lockdowns which spare rural county areas if recommended by NPHET.
Until now, lockdowns have applied to entire counties but a more targeted approach is being considered.
"First of all we have an opportunity to avoid those areas going to Level Three at all if we adhere to the public health guidance - reduce congregations, reduce the number of social contacts and wear masks in shops and on public transport," he said.
"NPHET will advise us in terms of any restrictions that may have to come in for other areas.
"They are concerned about urban centres - Cork, Limerick, Galway and Waterford - particularly as universities and institutes of technology reopen in the coming weeks."
"That is a concern - where you have high density populations the virus can thrive in such situations."
The UK has imposed such lockdowns on major cities and, in particularly, on university campuses where there have been major virus clusters.
Comment: Much like the flu at this time of year, only it would appear the flu is probably worse: UK: Three times more people dying of flu than coronavirus
Edinburgh and Glasgow have banned students from leaving their halls of residence to control the spread of the virus.
"NPHET may advise in terms of particularly localised restrictions though, to date, it has been on a county by county basis," Mr Martin said.
"The numbers are particularly growing in the cities and urbanised parts of those counties."
"That will ultimately be a matter for NPHET as it advises Government. But our objective is to say to people living in these locations - we can avoid having to go to Level Three. We can keep the numbers down. We can stabilise the numbers if we adhere to the guidance an all of us personally and collectively do things that will prevent the virus from growing."
"The rise of the virus has been within the community and within wherever large gatherings have happened," he said.
Comment: That's because it's infectious, and it is mutating to become even more so, meanwhile it's also becoming even more harmless.
Mr Martin said no one wanted to see restrictions imposed - but the spread of the virus had to be curtailed as winter approaches.
Comment: Coronavirus thrives during winter, and so they're setting themselves up for an impossible, pointless and wasteful task.
"It is a matter for NPHET and they will advise on those situations as they evolve."
"Suffice to say right now they are very concerned. I was speaking to the Chief Medical Officer over the week and in places like Cork city (cases) have been going up in a straight line in the past two weeks."
"That is a worry - between 20 and 30 cases a day. That is worrying. Likewise in other city areas."
Comment: Cases mean very little if the tests themselves are admittedly flawed and, even if they weren't, the vast majority, if they experience symptoms, it will be much like the flu.
"We are flagging that and making it very clear to people that those are danger areas right now. However, Cork is coming from a low base. There is an opportunity to stabilise it. It is in our hands basically and that is the message this week."
"The situation in relation to children - there is reassuring evidence generally across the school's system that children are not transmitting to children. They may bring it in from outside into schools but generally the Chief Medical Officer is satisfied with the situation in primary schools."
Comment: See also: Everything You Think You Know About Coronavirus...