The man started walking across to the other side of the road, away from the officers, and into the path of an oncoming car.
The police officers provided first aid until St John arrived but the man died a short time later.
Next of kin are still being notified, Johnston said.
"Our thoughts are with his family at this extremely difficult time and we will be ensuring they are supported," he said.
"This was a very upsetting incident for all involved, including our officers who were attempting to try and assist this man to safety and we are ensuring they are being offered welfare."
He said it was also a traumatising incident for the driver of the vehicle and they were being supported by Police.
Police are investigating and it had been referred to the IPCA and WorkSafe.