South Korea's military is 20 percent smaller than it was six years ago as the world's lowest birth rate shrinks the pool of men available for enlistment, according to a new report from the country's defense ministry.

South Korea's military has shrunk to about 450,000 people - a decline of 20% over the last six years, according to a defence ministry report released by a ruling party lawmaker on Sunday. Authorities say the main reason behind the decline is the country's dismal birth rate, which at 0.75 babies per woman is the world's lowest.

The shortfall, driven by the Asian country’s record-low birthrate of 0.75, left the military 50,000 soldiers under the level deemed necessary for defence readiness in 2025, the defence ministry said in a report on Sunday. More worryingly, it noted, there was a shortage of 21,000 non-commissioned officers.