Italian riders at the world track cycling championship in Roubaix lost bikes worth 10,000 euros ($11,600) each to thieves, local authorities told AFP on Saturday.
The local authorities said the bikes disappeared late on Friday or early on Saturday, but did not say how many had been stolen.
"They forgot the recommendation to leave the bikes in the velodrome until the end of the championships," Yannick Gomez, director of the departmental board for public safety, told AFP.
Gomez added a vehicle was parked outside the team hotel for "many hours" without surveillance as the bikes were stolen.
Heading into the last two days of the championships, the Italians topped the medal table with three golds and seven total medals.
The competition organisers told AFP all the racers who lost bikes had already finished their participation.
They also said the thieves took road bikes as well as track bikes, including some belonging to star time trialer Filippo Ganna.