Los Angeles is becoming a "Third World city" with immigrants making up half its workforce, says a new study.

A third of immigrants have not graduated from high school and 60 per cent do not speak English fluently, the Migration Policy Institute found.

It said this left immigrants ill-equipped to fill California's fastest-growing occupations, such as computer software engineering and nursing. The organisation added that as the so-called baby boomers reach retirement age, a similar pattern will spread across the US.

Ernesto Cortes Jr, of the Industrial Areas Foundation, a think-tank that specialises on social change, claimed Los Angeles was at a crossroads.

"The question is are we going to be a 21st century city with shared prosperity, or a Third World city with an elite group on top and most on near poverty wages?" he said.

The US Census Bureau last year predicted that by 2050, minorities will account for half of all residents across America.

It registered the largest numerical increases in minority residents in metropolitan Los Angeles, Riverside, in California, Dallas, Houston and New York.

In 2000, according to the Census Bureau, whites were in a minority in 262 US counties, up from 183 in 1990.

Nationally, the number of minorities topped 100 million for the first time in 2006, to make up about one third of the population.