An off-duty police officer and another female cyclist were seriously injured in a suspected hit-and-run incident Esperance while on a charity bike ride on Tuesday afternoon.

Esperance police are calling for witnesses to the incident which saw the cyclists thrown from their bicycles on Goldfields Road in the Esperance suburb of Castletown, at about 12.45pm.

Two cyclists have been struck down by a vehicle in a suspected hit and run in the Esperance suburb of Castletown. Credit:The Esperance Express

Senior Sergeant Richard Moore of the Esperance Police Station said three cyclists were riding south on Goldfields Road when two of them were hit by a red 1984-87 Mitsubishi Pajero.

"Three cyclists were heading south on Goldfields Road as they approached Reynolds Road," he said.