A police officer suffered significant head and facial injuries after a metal pole speared a divisional van in a horror early-morning smash on Swanston Street in Melbourne's CBD.

Two policemen, both from Melbourne East Police Station, were responding to a call to assist paramedics at 2.15am when their police van crashed into a pedestrian barrier at a tram stop between Federation Square and Flinders Street Station.

The 10-metre-long pole, which ran down the middle of the tram line to stop pedestrians from crossing between platforms, pierced the front windscreen and speared through the back of the van, effectively skewering the vehicle.

Both officers were injured, but the driver, a father of young children who had been in the job for three-and-a-half years, bore the brunt of the crash.