An adviser on education policies to Japan's right-wing government has sparked a furore by recommending that immigrants in the world's third-largest economy be separated by race.

In a column for the conservative Sankei newspaper, Ayako Sono said apartheid-era South Africa showed that whites, Asians and blacks should live apart. “Black people fundamentally have a philosophy of large families,” she wrote. “For whites and Asians, it was common sense for a couple and two children to live in one complex. But blacks ended up having 20 to 30 family members living in a single unit.”

She said black Africans had ruined areas previously reserved for whites in South Africa and they would do the same thing to Japan if allowed to do so. According to the Japanese media, the author has never lived in South Africa.

Ms Sono is a best-selling conservative author and a vocal supporter of Prime Minister Shinzo Abe's efforts to revive patriotic education. Abe appointed her to a panel on educational reform in 2013 but the government says she has since quit. She has also been quoted in a government-recommended textbook on morals for secondary school students, alongside Mother Theresa and other prominent figures.

The column, written on Japan's National Foundation Day, traditionally a holiday for expressing patriotism, sparked outrage, with online commentators branding it “disgusting” and “appalling”.

Japan's government is considering allowing 200,000 foreigners a year to enter the country to head off a growing demographic crisis. The country's population is aging and declining, falling by nearly a quarter of a million in 2013.

An advisory body to Abe said last year that opening the immigration drawbridge to more foreigners would eventually help stabilise the population – currently 127 million – “at around 100 million”.

The Asian powerhouse has so far shunned the mass immigration policies of other developed economies. Less than two per cent of the population is foreign, and that includes hundreds of thousands of long-term residents from China and Korea.