Decked out in brightly-coloured costumes and watched on by thousands of cheering spectators, competitors carrying homemade flying devices leapt off a platform above an Australian river in a quirky annual competition Sunday.

The Birdman Rally, which raises funds for charities, is held at Melbourne's Yarra River and involves participants flying homemade gliders without mechanical assistance.

Contestants jump off a four-metre  platform above the river, staying in the air for as long as possible before crashing into the water.

They are judged for their costumes, pre-jump performances and how far they fly and fall. The amount the contestants raise for charities before their flights also contribute to their total distance.

While past contestants have turned up in bizarre costumes, including 2017's winner whose parachute was made out of bras, this year's entrants arrived with more traditional-looking contraptions shaped as planes and gliders.

Winner Daniel Mazzei, who called himself the Red Baron after the ace World War I German fighter pilot, plunged into the Yarra with a bright red plane on his back.

"No, I didn't think I would jump as far as I did that's for sure," Mazzei, a builder by trade, said after claiming the trophy.

Mazzei raised money for Bravehearts, a charity that supports victims of child sex assault.

The contestants collected a total of almost Aus$100,000 for nominated charities, organiser the City of Melbourne said.