Olympic gold medallist Ed Clancy is among a host of top British cyclists taking part in the Halfords Tour Series in Aberystwyth.
It is the first time the series has visited Wales, with the main race having started at 1900 BST.
Among the other top riders taking part is Sweden's Magnus Bäckstedt, a Tour de France stage winner.
The eight-race tour started in Durham on Tuesday and ends at Canary Wharf in London on 16 June.
In Aberystwyth, races for school children and local cycling clubs begin at 1400 BST.
They are being given the chance of competing on the same town circuit as the professional riders.
Clancy, 26, is probably the biggest name taking part in the event.
As well as being Olympic team pursuit champion, Clancy won gold at the Track Cycling World Championships in Denmark last year, and he also picked up the men's omnium - the "pentathlon" of cycling - in the second round of the World Cup in Cali, Colombia.
He is joined by Bäckstedt, 36, a Tour de France stage winner and a winner of the professional one-day road race in northern France, the Paris Roubaix. He lives in south Wales.
Beijing Olympics individual pursuit bronze medallist Steven Burke, 23, and Rob Hayles, 38, who won silver in the team pursuit at the Athens Olympics and a bronze at the Sydney Olympics, are also taking part.
The Welsh leg of the cycling tour series has received £15,000 from the Welsh Government.
Ceredigion council leader Keith Evans said: "This is a fantastic opportunity to showcase Aberystwyth as a vibrant tourist destination and a diverse area in which to live.
"I hope locals and visitors alike will turn out in force to see for themselves what the town has to offer."