There were nearly 7000 notifications of gonorrhoea, a serious infection of the genital tract, in 2016, up 28 per cent on the previous year's figure - the largest annual increase since 2012.

While the figures reflect the higher number of tests being performed on multiple sites of infection on the body, this only rose by 13 per cent, meaning there was a definite jump in gonorrhoea cases.

"The data show that more can be done in terms of condom use, which is the best way to prevent the transmission of an infection," said Dr Christine Selvey, a medical epidemiologist at NSW Health.

"Both gonorrhoea and chlamydia can lead to pelvic inflammatory disease, and apart from being painful, women can get scarring which may later lead to fertility and pregnancy problems."

The NSW Sexually Transmissible Infections Data Report for 2016 shows 81 per cent of gonorrhoea notifications were in men. Gonorrhoea is more common among men who have sex with men.

But the largest relative increase in the gonorrhoea notification rate was in females - up 43 per cent, compared to 23 per cent for men.

"We use women as bit of a marker for the heterosexual population, so the fact we have seen this increase suggests we're seeing more transmission in heterosexual people as well," said Dr Selvey.

The number of chlamydia cases also rose in 2016. There were 337 notifications per 100,000 people, a 13 per cent increase on the 2015 figure. Interestingly, NSW Health observed a change in trend by gender.

"In 2016, the rates of chlamydia notification in both males and females were very similar, whereas in previous years the female chlamydia notification rate was consistently higher than males," the report said.

The report also shows the infectious syphilis rate remains stable.

Dr Christopher Bourne, head of NSW STI Programs Unit at NSW Health said much of the increases reflected the "big ramp-up" in service delivery to encourage more testing.

"So we're seeing lots more testing, more frequent particularly in high-risk populations and testing in different anatomical sites, depending on how people are having sex," he said.

"We're having more comprehensive, more frequent testing, so I would expect we're finding infections that we weren't finding before."

He said increased testing meant people could find out they were infected before they showed symptoms and take action so that gonorrhoea, for example, didn't lead to septicaemia.

He said NSW Health would continue to consistently send out messages to the public about the importance of using condoms.

The report shows the proportion of gay men with casual partners reporting consistent condom use has fallen, from 47 per cent in 2014 to 42 per cent last year.

Chief Health Officer Dr Kerry Chant said condoms were the most effective way to prevent the transmission of STIs.

"NSW Health has invested in a variety programs promoting condom use across all age groups, through online and social media platforms as well as face-to-face education," Dr Chant said.

"This includes the ACON Condom and ACON Choose Prevention Campaigns, which target gay and homosexually active men."