Children aged up to three years are more at risk of developing autism when exposed to toxic air pollutants, an Australian study shows.

Young children exposed to toxic air pollutants are significantly more likely to develop autism, new Australian research reveals.

The study of nearly 1500 children in China, aged up to three years, found those exposed to fine particles from some outdoor pollutants were up to 78 per cent more likely to develop autism spectrum disorder.

Vehicle exhausts, road dust and emissions from factories and construction works are among such pollutants.

The Monash University study was conducted over nine years in Shanghai and involved 1444 children, 124 of whom had autism.

Melbourne-based Associate Professor Yuming Guo, who led the research published in Environment International on Tuesday, said the causes of autism are complex and not fully understood.

But he said young brains are more vulnerable to toxic exposure, and studies suggest brain function and the immune system can be affected.

"These effects could explain the strong link we found between exposure to air pollutants and autism spectrum disorder," he said.

"But further research is needed to explore the associations between air pollution and mental health more broadly."

The research looked at three sizes of particles - referred to as PM1 (the smallest variety), PM2.5 and PM10.

Prof Guo said PM1 contributed to an even greater risk of children developing autism, and he hoped the study will prompt countries to develop standards relating to the tiny particle, like those currently in place for some larger particles.

There is no safe level of exposure to air pollutants, which have links to pre-term births, delayed learning and serious health conditions, Prof Guo added.

"All countries should pay attention to reducing air pollution and improving air quality, to increase their life quality and improve their health outcomes."

The new study is understood to be the first to examine the effects of long-term exposure of air pollution on autism during the early years of a child's life in developing countries.

More than four million people die each year from outdoor air pollution, the World Health Organisation states.

The deaths are mainly due to heart disease, stroke, chronic obstructive pulmonary disease, lung cancer, and acute respiratory infections in children.