The US population will double in the next 100 years, according to predictions by the US Census Bureau.

From an estimated 275 million people in 2000, the Bureau projects there will be 571 million in the year 2100.

However, even such a sharp increase might not mean acute overcrowding because of the large amount of land still underdeveloped for residential use in the US.

"If you look at the density for the United States, we are not even coming close to the densities that you see in Europe," said Census statistician Tammany Mulder.

Even the projected figure for 2100 would only be about a quarter of the current population density of Germany or the UK.

Much of the increase in population is expected to come from immigrants.

"The increasing number of potential parents and continued migration from abroad would be sufficient to add nearly 300 million people during the next century," Frederick Hollmann, demographer at the Bureau's population projection branch, said.

Overall, the population will be older - with some 5.3 million over the age of 100.

The projections also show more women than men in the next century. A higher percentage of the elderly are expected to be women, who generally live longer than men.

Ethnic shift

The Bureau predicts that by 2059 whites will form less than 50% of the total population.

Hispanics are set to continue the demographic rise they began over the past decade.

They made up 9% of the population in 1990, growing to 12% before the end of the decade.

By 2005, Hispanics are expected to match and then overtake the black population, currently at 13%.

By the end of the century, a third of Americans are projected to be Hispanic.

The bureau also projects the number of Asians and Pacific Islanders will more than triple in 50 years to 38 million, or 9%, from an estimated 11 million or 4% in 1999.

By 2100, they are projected to reached 75 million, or 13%.

"The Hispanic and Asian populations grow faster as a result of birth rates and net migration," Mr Mulder said.

"Hispanics generally have higher fertility rates and Asians have high net migration rates to the US."

For example, a Hispanic woman of child-bearing age had an estimated 2.9 babies in 1999, compared with 1.8 babies for a white woman, and 2.1 for a black woman.