Chinese people are projected to live for over 80 years on average by 2040 when its global ranking on life expectancy will surge, according to a study by medical journal The Lancet.

China will be among 59 countries expected to have a life expectancy of over 80 years by 2040, according to the study, and the country's global ranking on life expectancy will rise from 68th to 39th.

It predicts that Japan, Singapore, Spain, and Switzerland would have a life expectancy of over 85 years by 2040.

The bottom of the list is dominated by African countries such as the Central African Republic, Somalia and Zimbabwe, where life expectancy will be under 65 years.

Among the developed countries, the ranking of the US will see the sharpest decline, from 43rd to 64th, with life expectancy rising just over a year - from 78.7 in 2016 to 79.8 in 2040.

The study took into consideration 250 causes of death in 195 countries and regions between 2016 and 2040.

According to the study, most indicators of health are forecast to improve by 2040 globally, but 36 are forecast to worsen, such as high body-mass index.

Deaths from accidents and non-genetic diseases such as lung cancer and Alzheimer will increase.

The topic has triggered heated discussion on Chinese social media platform Weibo. By noon on Friday, topics with hashtag "life expectancy by 2040" have been read 28 million times.

"I will try to eat healthy and have a regular routine from now on, to reach the expected life expectancy of China," an internet user said on Weibo.