Japan, which has held the top spot for the world's longest living citizens, is expected to be surpassed by Hong Kong in 2045, according to projections in a U.N. population report released on Thursday.

"It is notable that Japan certainly came from behind during the late 20th century and became the country with the highest levels of life expectancy and now we observe other countries in Asia with very rapid increases," John Wilmoth, director of the population division of the U.N. Department of Economic and Social Affairs, told reporters.

"World Population Prospects: the 2012 Revision" reported that Japan, which most recently held the No. 1 spot for life expectancy with citizens living to be 82.7 years on average, would change by 2045-2050.

During that five year period, data suggest that Hong Kong will overtake the No. 1 spot with its population expected to live to be 89. South Korea and Japan will follow with citizens in their respective countries living 88.4 years.

From 2005-2010, Hong Kong was ranked second after Japan, with its people living to be 82.4. The recent uptick in the longevity of women in Hong Kong is a factor, said Francois Pelletier, chief of population estimates and projections.

In a 2012 report by Japan's health ministry, women from Hong Kong overtook Japanese women, who had previously held the No. 1 spot for 26 years.

Even though Japan is projected to fall behind South Korea (95.5 years) and Hong Kong (94.9) in 2095, the country would still be ranked third (94.2).

Wilmoth attributed a "combination" of reasons for Japan's long-held position. Among them was the fact that as a "more egalitarian society," there were fewer differences between the rich and poor and its citizens live a "relatively healthy" lifestyle.