A fifth of the Japanese workforce faces the risk of death from overwork, according to a new government survey into the country's notoriously strenuous working culture.

Hundreds of deaths related to overwork -- from strokes, heart attacks and suicide -- are reported every year in Japan, along with a host of serious health problems, sparking lawsuits and calls to tackle the problem.

The survey was part of the nation's first white paper on "karoshi", or death from overwork, endorsed by Prime Minister Shinzo Abe's cabinet on Friday.

While the popular image of Japanese salarymen toiling long hours for the company before taking the last train home is changing, many still spend far more hours in the office than counterparts in other modern economies.

According to the paper, 22.7 percent of companies polled between December 2015 and January 2016 said some of their employees logged more than 80 hours of overtime each month -- the official threshold at which the prospect of death from work becomes serious.

The report added that approximately 21.3 percent of Japanese employees work 49 or more hours each week on average, well above the 16.4 percent reported in the US, 12.5 percent in Britain and 10.4 in France.

The survey concluded that Japanese employees also reported feeling high levels of stress related to their work, pushing officials to call on companies to improve working conditions.