HIV diagnoses have reached a 20-year high in Australia and there are fears one in seven people with the virus do not know they have it, putting more people at risk.

Public health experts are calling for a renewed focus on HIV testing and treatment after new data showed 1235 people were diagnosed with the blood-borne virus in Australia last year - a 70 per cent increase on the number documented in 1999 when diagnoses were at their lowest.

HIV infection rate rising: Fears one in seven people carry the virus.

The Annual HIV Surveillance report produced by the University of NSW’s Kirby Institute said unprotected sex between men continued to be the main driver, causing about 70 per cent of new diagnoses between 2009 and 2013. About 25 per cent of transmissions were through heterosexual sex and 2 per cent were through injecting drug use.

Of 313 diagnoses believed to be caused by heterosexual sex last year, about half of the people involved were from countries where HIV is more prevalent. On average, about one child each year for the last decade has been born with HIV in Australia, having acquired it from their mother.