A witness says the rider was coming from Avatiu going straight into the Ports area when he was hit by a van.
A number of people rushed to support the injured man before emergency services attended the scene.
The man was taken to hospital for the treatment of a head injury.
A police spokesperson says the driver of the van admitted to police that he failed to give way. He was immediately charged with careless driving causing injury.
The section of road has been the scene of multiple car and motorbike accidents, with drivers often not taking care to give way to their right.
Other drivers have also driven too quickly along the section of road and have collided with the roundabout.
A give way sign was installed in August after Cook Islands Road Safety Council president Brent Fisher and local businesswoman Jackie Rongo petitioned Infrastructure Cook Islands (ICI) and the police for an upgrade for the roundabout.
Following yesterday’s accident Rongo says she hopes ICI will take action with their proposed solutions to make the roundabout safer as soon as possible.
She says the intersection needs urgent action, as during the fast-approaching festive season, there will be returning Cook Islanders and tourists on the roads who may not be aware of the dangers posed by the roundabout.