Spain by 2050 will be a depopulated nation dominated by elderly and single people, according to a report that predicts the country will have lost 5.3 million inhabitants, or 11% of the current population, by the middle of the century.

Spain’s low birth rate and high life expectancy are seen as a demographic problem that the report, released by the national statistics office on Thursday, expects to become more entrenched.

If the trends continue, by 2050 the over-65s will make up 34.6% of the population, while close to a quarter of a million Spaniards will be over 100 years old. By that date there will be 1.7 million fewer children under 10 than there are today.

A country also once famed for large families seems destined to become a nation of singletons, with single-person households rising by about a fifth over the next 15 years, to make up 28% of the total. Two-person households will make up a third of the total.

While the fertility rate is predicted to rise slightly, from 1.33 to 1.38, births will fall overall because there will be fewer women of childbearing age. The average age at which Spanish women have their first child is expected to rise from 31.9 to 33 years.

In the first 10 years of the millennium, immigration from Latin America, north Africa and elsewhere in Europe boosted Spain’s reproductive population, but following the financial crisis hundreds of thousands of those immigrants have returned home. Meanwhile, large numbers of young Spaniards have themselves emigrated in search of work. However, immigration is predicted to slightly exceed emigration in the coming years.

In 1900 life expectancy in Spain was 35, meaning that half of those born did not live to be 15. Life expectancy is now 80 for men and 85 for women; if the trends continue, by 2065 this will rise to 88 and 91 respectively.

Demographers stress that elderly people should not be seen as burdensome on Spanish society. “They have resources, 70% have paid off their mortgages,” said Julio Pérez Díaz, a demographer at the Centre for Human and Social Sciences in Madrid. “They are big consumers and during the long financial crisis it has been pensioners who, above all, have saved their children and grandchildren from going under.”

Antonio Argũeso, of the institute that produced the paper, cautioned: “These are not so much predictions but references to the way things might evolve. In the 1990s we didn’t think Spain would arrive at a population of 40 million but no one had predicted that 10 years later six million immigrants would arrive and take the population to 47 million.”