Photos have been released of a man suspected of assaulting and robbing an elderly man in Auckland as police try to hunt the alleged offender down.

The elderly man was attacked on July 29 in Sylvia Park, and his watch and wallet were stolen. The man was hospitalised with non-life threatening injuries.

Inquiries have been ongoing since the incident occurred, which have identified the offender boarding a train at the shopping centre at 5.55pm immediately after the robbery took place.

Another image of the man. Photo / Supplied

Police said he got off the train at Panmure Train Station, before boarding a bus heading towards the central city at 6pm.

Investigations have not led police to identify the man, so now they are asking the public for help.

Detective Senior Sergeant Greg Brand said the attack was "incredibly callous" and targeted a vulnerable person.

"Police have no tolerance for this sort of act and we ask anyone that knows this man to contact Police via our 105 phone service or online."

Witnesses said the seriously injured man appeared to be aged late 60s or early 70s. They also told the Herald at least five men took part in the incident.

The witness said he saw the victim lying on his side, limp and bleeding profusely from his mouth while his wife sat over him in shock.

One bystander at the scene reported that the elderly man was "bleeding like crazy". Another man said "it was the most amount of blood I have ever seen".

The unnamed witness said the large amount of blood was due to two lacerations on the elderly man's face and a suspected broken nose. He had also been taking blood-thinning medication.

The attackers were seen fleeing the incident on foot. No one has been arrested.

A police spokesperson said the victim was knocked to the ground and suffered serious injuries.