There were 101 HIV diagnoses among gay and bisexual men in the first half of this year - the lowest recorded in NSW since HIV emerged in the 1980s.

"We've seen new diagnoses among gay and bisexual men falling steadily for 12 months now despite an increase in HIV testing and we're confident this means HIV transmission is dropping," said NSW Chief Health Officer Dr Kerry Chant.

"This is a great achievement [and] we're a step closer to achieving our goal of virtually eliminating HIV in NSW by 2020."

The latest data shows there were 217 new cases in the past financial year, which is 25 per cent less than the average of the previous five years.

Dr Chant said this drop reflected the combined efforts of doctors, researchers, the government and affected communities to drive down infection rates through increased testing, early detection and fast treatment.

A major factor was the rapid uptake of Pre-Exposure Prophylaxis (PrEP), a drug proven to prevent the transmission of HIV.

While more tests are being conducted, the number of people diagnosed late has remained stable, meaning there are still people with undiagnosed HIV in the community.

"These people have not had the benefit of accessing and being on treatment and therefore preventing transmission, so we need to do more," said Dr Chant.

"We also need to redouble our efforts to reach heterosexual people and gay and bisexual men born overseas for HIV prevention and testing because we haven't seen a fall in new diagnoses in these groups."

NSW has become a world leader in the prevention of HIV, a virus that attacks the immune system and can lead to AIDS.

Nicolas Parkhill, chief executive of AIDS Council of NSW (ACON), said the results of NSW's HIV strategy were "unprecedented".

"We have seen decreases in other international jurisdictions but not at the scale and not at the speed that we've seen here," he said.

"Often those decreases have occurred in cities such as San Francisco or New York City, but this is a state-based report of 7 million people, which is quite extraordinary."

Professor David Cooper of UNSW's Kirby Institute, which is running the PrEP trial, said the drug needed to be made available for high-risk groups in all states.

Last week, the Pharmaceutical Benefits Advisory Committee deferred its decision to place PrEP on the Pharmaceutical Benefits Scheme, citing high costs and the need for more information.

"The results released today provide strong evidence to support wide availability of PrEP," said Professor Cooper.

The data also shows in January to June this year there was a 39 per cent drop in the number of gay and bisexual men diagnosed with HIV where they had acquired it within the previous 12 months, compared to the same period over the past six years.

Marco Matillano joined the PrEP trial last year, which involves taking one pill each day. He said until an HIV scare in his mid-20s, he thought he was "invincible".

"I had unprotected sex with another man and he told me two weeks later that he only just found out that he was HIV positive and I remember all those feelings of anxiety and thought, 'I'll never make that mistake again'," he said.

"What I love about PREP is I'm looking after my own health in a proactive way and all those times it gets spontaneous and you aren't particularly careful in the heat of the moment, I have that reassurance that I'm doing something about it."

Craig Cooper, chief executive of Positive Life, a non-profit representing people with HIV, said more work needed to be done to reduce people's fears about HIV.

"We need to cut through the fear and the paranoia of what HIV is as an infectious disease," he said.

"We need to combat the fear and to trust the system, we need to trust the doctors and we need to trust the health system to be able to work with us to turn this around."