According to the Central Statistics Office, the population could reach 6.7m over the next 23 years, a 2m-plus increase from its current level.

A new report from the CSO points out that the area representing the Republic of Ireland registered a decline in population, from just over 6.5m in 1841 to 3.1m in 1999.

The effects of the Famine of 1846-1847 and heavy population losses due to emigration in the latter half of the 19th century contributed to the dramatic decline.

Despite the return of outward migration in recent years, the population has continued to grow strongly, mainly due to the high number of births.

Ireland has the highest birth rate in Europe at 2.1 per woman and is expected to stay in or around that level over the next few decades.

Looking at the most optimistic migration scenario, the CSO sees a return to a positive migration flow by 2016 at +18,200 a year and increasing steadily before settling at +30,000 (70,000 immigrants/30,000 emigrants) by 2021.

Currently, more people are leaving the country than coming here. Last year, 87,000 people left and 53,000 arrived here, an overall decrease of 34,000.

However, the report warns that migration flows are hugely influenced by the economy and emigration could continue to exceed immigration in the years ahead, levelling off at minus-5,000 from 2021 to 2046.

The report predicts a recovery in the number of men aged 25 to 44 participating in the labour force by 2021 and an increased in the number of men aged 60 and over.

While gains made by married women in the labour market will level off, the number of women, particularly those who are single, will recover by 2016, with minor gains made thereafter.

Life expectancy is expected to increase from 77.9 years in 2010 to 85.1 years by 2046 for men and from 82.7 years to 88.5 years for woman.

The number of people over the age of 65 is set to increase very significantly from its 2011 level of 532,000 to between 850,000 and 870,000 in 2026. By 2046, the older population will have exceeded 1.4m.

The very old population — those aged 80 years and over is expected to increase dramatically from 128,000 in 2011 to between 484,000 and 470,000 in 2046.

The young population at 976,600 was considerably higher than the old population at 531,600 in 2011. However, the trend will reverse by 2031.

The CSO expects that there will be more older persons than younger persons in any event by 2036 and by 2046 there will be between 112,000 and 561,000 more older people than younger people, depending on the scenario that applies at the time.