In a move to promote safe sex, a New South Wales health promotion organisation has put a giant pink condom onto the obelisk at Sydney's Hyde Park.

The 18-metre tall condom was put onto the heritage-listed structure on Friday night in the lead up to the Sydney Gay and Lesbian Mardi Gras, to be held next month, by lesbian, gay, bisexual, transgender and intersex (LGBTI) health promotion organisation ACON.

The organisation's chief executive Nicolas Parkhill said the Mardi Gras was a good time to remind people that using condoms was one of the most effective ways to stop transmission of HIV.

"Every year around 80 per cent of HIV transmissions in NSW are among men who have sex with men, so it's vital that we use opportunities like Mardi Gras to remind gay men about the health benefits of using condoms," Mr Parkhill said.

"While new drugs are starting to provide other means of protection against HIV, condoms remain central to the fight against the virus because they remain one of the most cheap and effective ways of preventing the transmission of HIV and other sexually transmissible infections."

He said the giant condom was first put up for World AIDS Day in 2014.

A large pink condom is put in place on the tall structure in central Sydney. ( ABC News )

"It was a huge hit ... so we thought we'd roll it out again for this year's Mardi Gras to act as a highly visible safe sex reminder, not just for locals but also for the thousands of international visitors who come to Sydney for Mardi Gras."

ACON also held a launch for its Stay Safe campaign at Bondi Beach today, as part of efforts to put an end to HIV transmissions in NSW by 2020.

The organisation gave away 1,000 pink inflatable rings, which they called "lifesavers" and described as "condom-like" to the public at the beach.

Established in 1985 as the AIDS Council of NSW, ACON works to end HIV transmission among gay and homosexually active men, and promote the lifelong health of LGBTI people and people with HIV.

It is funded by the NSW Government through the NSW Ministry of Health.

The obelisk was built in 1857 to vent Sydney's first sewerage system and now provides ventilation for the city's stormwater system.