Motorists are being warned of delays after a serious crash involving a vehicle and a pedestrian in central Auckland.

Police said they were called to the crash site at the intersection of Melrose and Hayr Roads in Hillsborough just before 3.30pm. The Serious Crash Unit remains at the scene.

Hayr Rd is closed and diversions are in place at Littlejohn St and Olsen Ave, Melrose Rd and Stamford Park Rd, police said.

Drivers were asked to find alternate routes and to expect delays.

Hato Hone St John sent two ambulances, a critical care unit and an operations manager to the scene at 3.25pm.

A spokesperson said one patient was taken to Auckland City Hospital in a critical condition, while two others were taken to Starship Hospital in a moderate condition.

Another person with minor injuries did not require transport to hospital.