Up to 40 shots were fired in the deadly Manus Island violence as local Papua New Guinea guards went on a killing spree with the intent to kill every asylum seeker, an Australian guard has described in his submission to an inquiry into the attack.

The G4S guard, who has asked to remain anonymous, has graphically detailed the bloodshed of the February violence, saying the 23-year-old asylum seeker who died in the attack, Reza Barati, was kicked in the head numerous times before being hit with a lump of wood by a local PNG "Spic and Span" cleaner.

"I was told later that Reza had died," the guard said. "IHMS (International Health and Medical Services) staff at The Bibby (the floating hotel for staff) got him breathing again but his injuries were quite severe and he died.

"I was under the belief they wanted to kill every single one of the clients.''

The guard said he also believed it was the PNG police who fired between 20 and 40 shots on the night of the violence. And it was the police who then made an attempt to collect every shell casing that had been fired – "I believe to cover up their actions that evening."