Autism rates in the US are rising fastest among Hispanic and black children, a new study finds.

Researchers say that rates of the developmental disorder in children born between 2007 and 2013 rose 73 percent among Hispanics and 44 percent among blacks.

Meanwhile it increased just 25 percent among white children - albeit a surprise after it plateaued in the mid-2000s.

The team, from the University of Colorado Boulder, says that, although some of the rise can be attributed to better outreach and diagnosis among minority populations, it believes other environmental factors are involved.

A new study from the University of Colorado Boulder has found that autism rates rose 73% among Hispanics and 44% among blacks in children born between 2007 and 2013 (file image)

Autism spectrum disorder (ASD) is a developmental disorder in which sufferers have a hard time communicating and with behavior.

It encompasses several conditions - including autism, Asperger's syndrome and childhood disintegrative disorder - and symptoms can range from mild to severe.

Children are usually diagnosed by age two after they exhibit signs such as reduced eye contact, not responding to their name and performing repetitive movements.

According to the Centers for Disease Control and Prevention, about one in 59 children has ASD, with boys much more likely to be diagnosed than girls.

'We found that rates among blacks and Hispanics are not only catching up to those of whites - which have historically been higher - but surpassing them,' said co-author Dr Cynthia Nevison, a research scientist at the University of Colorado Boulder.

'These results suggest that additional factors beyond just catch-up may be involved.'

For the study, published in the Journal of Autism and Developmental Disorders, the team analyzed data from the Individuals with Disabilities Education Act (IDEA) and the Autism and Developmental Disabilities Monitoring (ADDM) Network.

IDEA tracks rates among three-to-five-year-olds in all 50 states every year, while ADDM looks at prevalence among eight-year-olds in 11 states biannually.

Researchers found that, by 2012, rates in black children were higher than in white children in 30 states.

Meanwhile, Hispanic rates were growing faster than any other racial group.

In states classified as 'high prevalence', one in 79 whites, one in 68 blacks and one in 83 Hispanics born in 2013 had an autism diagnosis by age five.

'Our data contradict the assertion that these increases are mainly due to better awareness among minority children,' said co-author Dr Walter Zahorodny, an autism researcher and associate professor of pediatrics at Rutgers New Jersey Medical School.

'If the minority rates are exceeding the white rates, that implies some difference in risk factor, either greater exposure to something in the environment or another trigger.'

For future studies, the researchers plan to try and identify any others factors that could be behind the rising rates.