The majority of children born in the US now belong to minority ethnicities, according to Census Bureau data released on Thursday that show the country is entering a new era of diversity.

The white proportion of the population has been declining as the Hispanic population in particular has grown sharply, a development that has contributed to a heated national debate about illegal immigration.

The Census Bureau reported that minorities – including Hispanics, African-Americans, Asians and people of mixed race – comprised 50.4 per cent of all births in the year to July last year, while non-Hispanic whites made up 49.6 per cent.

“This is an important landmark,” Roderick Harrison, a former chief of racial statistics at the Census Bureau, now a sociologist at Howard University, told the Associated Press. “This generation is growing up much more accustomed to diversity than its elders.”

The data were part of the first set of population estimates by race, Hispanic origin, age and sex released from the 2010 Census.

Minorities made up 36.6 per cent of the US population as a whole, or 114m people, up from 36.1 per cent the previous year.

Hispanics are the most populous minority group, numbering 52m in 2011, and they are also the fastest growing ethnicity, with their population increasing by 3.1 per cent from the previous year.

California had the largest Hispanic population in the country, at 14.4m, but New Mexico had the highest percentage of Hispanics at 46.7 per cent.

The statistics were released as the Supreme Court considers the Obama administration’s challenge to Arizona’s controversial state law cracking down on illegal immigrants, giving law enforcement authorities the power to ask for documents from anyone they suspect of being in the country without authorisation.

The court is due to issue a decision in late June.

But five other states and numerous other local governments have enacted their own version of Arizona’s law, tired of waiting for the federal government to act.

“We remain in a dangerous period where those appealing to anti-immigration elements are fuelling a divisiveness and hostility that might take decades to overcome,” Mr Harrison said.

President Barack Obama campaigned in 2008 on a pledge to comprehensively reform the US’s immigration system, providing a path to citizenship for many of the estimated 12m illegals in the country, winning him the overwhelming support of the Hispanic community.

However, preoccupied with other political priorities such as the economy, and stymied by a gridlocked Congress, he has made no progress on immigration reform. In fact, deportations have skyrocketed under his administration.

The Census Bureau data showed that African-Americans comprised the second largest minority group in the US, at 43.9m in 2011, up 1.6 per cent from the previous year, with New York having the largest black population of any state.

When it comes to population growth, Asians, who numbered 18.2m nationally in 2011, were the second fastest-growing minority group, with their numbers rising by 3 per cent from 2010.

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