The man aged in his 50s suffered non-life threatening injuries when he was struck by a white Holden station wagon while helping people queuing at the Collingwood CoHealth testing site on Tuesday morning.

The driver then fled the scene.

A nearby nurse provided first aid to the Tarneit man until an ambulance arrived.

A short time later, police found the station wagon and arrested the male driver in Carlton.

He is being questioned by police.

CoHealth chief executive Nicole Bartholomeusz said the incident had sent "shockwaves" through the community and the COVID-19 testing clinic would be closed until Thursday.

"We are providing support and counselling to staff who were present when the incident occurred. We are also reaching out to clients and neighbours who may be affected to make sure counselling is available to them," Ms Batholomeusz said.

"This is an incredibly distressing event, and our thoughts are with the coworker and their family."

Police have called for anyone with information or dashcam footage to contact Crime Stoppers.

It's believed witnesses saw the vehicle driving erratically near the Melbourne CBD.

Australian Associated Press