At approximately 11:45am on Wednesday, Greenwich Police received a call for service involving a collision between a truck and a bicyclist on Shore Rd near the intersection with Grass Island.
Police say the bicyclists sustained serious injuries after being struck by the truck.
The truck was a Town of Greenwich Dept of Public Works truck.
The Greenwich Police Traffic Reconstruction Unit responded to the collision and are investigating the incident.
The scene was cleared at approximately 2:30pm.
The case is still under investigation. The pubic information officers said they will share a release when the investigation allows.