A gang of bicycle thieves is believed to be targeting patrons at the Australian Open, with reports that up to 10 bikes were stolen from outside the grand slam tournament in just one day last week.

Bicycle Victoria has issued a warning to cyclists after receiving numerous reports of robberies at Melbourne Park in the past few days.

Bicycle Victoria spokesman Garry Brennan said one man whose bike was stolen had returned to a bike rack at Melbourne Park to find five locks had been cut through and were lying on the ground.

"Another cyclist said the police had told him that they'd had 10 reports [of bicycle thefts] on one day," Mr Brennan said.

"If it is 10 bikes then it has almost got to be an organised gang."