Japan's population fell at the beginning of this year at the fastest pace since 1968, when the earliest comparable figures started getting collected.

As of January 1, the number of Japanese people (excluding resident foreigners) fell by a record 308,084 from a year earlier to 125,583,658, marking the eighth consecutive year of declines, government data showed Wednesday.

These changes highlight a mounting demographic challenge to Japan's economic growth that has been roughly two decades in the making. Some economists even call the situation a "demographic time bomb," given the vicious cycle that has formed between low fertility rates and low consumer spending.

The conflict lies in the tension between Japan's traditional work culture — which emphasizes the role of men as primary breadwinners — and younger generations' desire to have flexibility in their personal and professional lives.

Younger people increasingly want more egalitarian relationships in which men and women can both pursue their careers and share household duties. But career pursuits have won the battle for the last decade or so, while starting or growing families has taken a backseat on a mass scale.

The number of births in Japan fell 2.9% from the previous year to 981,202 today, the lowest since comparable data became available in 1974. People at or above the age of 65 account for 27.2% of the total population, the highest ratio on record, while those 14 or younger make up just 12.7%, the data showed.

The number of registered foreign residents in Japan increased 6.9% from a year earlier, according to the data. Japan has long been reluctant to open up to immigration, since many Japanese people pride themselves on what they see as their cultural and ethnic homogeneity.

But recently, the government has been increasing its efforts to attract students and high-skilled workers from overseas.

The overall population, which combines both Japanese and resident foreigners, fell 0.1% from a year ago to 127,907,086, the data showed.

Stanley White contributed to this article.