The West Coast population is expected to be lower in 2048 than it was in 2018.
Data released by StatsNZ shows the region's population in 2018 was 32,400 and it is predicted to be 30,600 in 2048.
The West Coast is the only region in the country to have a lower projected population.
The population dip will likely be the cause of more deaths than births and low net migration, a StatsNZ spokesperson said.
It projects deaths could exceed births on the West Coast by 50 a year in the early 2030s, and by 180 a year in the late 2040s.
The West Coast's population has dropped before, in 2001 and 2002 when it fell to 31,100.
According to data from the 2018 Census, the most common age group in the region is 55 to 59-year-olds.
They made up 2724 of the 31575 people who took part in the survey.
Development West Coast chief executive Heath Milne said the projections are based on the aging population in the region.
He said in the last ten years, the over-65 age group has increased by 2000 and the under 65 has decreased by 2600.
"As people get older, they're unable to add to the population so it's just about net migration and getting some skilled workers here."
Grey District Mayor Tania Gibson said they are concerned about it, but are unsure if the projections will end up accurate.
"What I've been seeing and what I've been hearing around the community, the moving of house prices and people moving into the district so we don't really know at this stage."
She said she thinks the West Coast's future population will come down to Government legislation.
"I think that the West Coast economy, like a lot of rural economies, is getting really hard done by Government policy.
"It's a real battle of keeping employment at the moment, we seem to be going very well but it depends on the different legislations that come through."