Hyde Park and Oxford Street in central Sydney are packed with glitter, lights and outlandish costumes for the annual LGBT celebration.

Sisters Laura and Jacinda Purcell from Penrith have been coming to the festival for years but it's their first time marching in the parade.

"I've been coming to Mardi Gras every year since I was 14," says Laura.

"We just love everything about it - that feeling of being accepted by everyone."

As per tradition, the "dykes on bikes" will kick off the parade on Saturday evening.

James Cowin and George Stephan travelled from Brisbane to march in the parade.

"We came last year and it was amazing," said Mr Cowin.

"It's such a positive experience but it also highlights such important issues," Mr Stephan said.

The parade is expected to draw more than 12,000 punters across four hours.

Of the 191 floats in the parade, several will focus on climate change while Australia's bushfire crisis "heroes" will be front and centre.

Wade Young is marching in the parade as part of a group called Cosplay Out Of The Closet.

"This is the first time we've marched in the parade and we can't wait to see what sort of reception we get," he said.

Parade creative director Kat Hopper said this year's "What Matters" theme seeks to stoke debate around social justice, trans rights, sustainability, climate change and love.

Grammy Award-winning UK singer Sam Smith will headline the afterparty alongside American pop performer Kesha and Brazilian drag queen Pablo Vittar.

The parade has drawn a high-visibility police presence, with the riot squad assisted by officers on horseback and members of the sniffer dog unit.

The parade commemorates the '78ers, a small group of protesters who were arrested and beaten by police when they tried to march as part of international gay celebrations back in 1978.

Australian Associated Press