A corrections officer has told the inquest into the death in custody of Indigenous man David Dungay that it was not "excessive" to call in a specialist squad to stop the inmate eating crackers.

Mr Dungay, 26, died on December 29, 2015, in Sydney's Long Bay Prison Hospital after being forcibly moved to an observation cell, restrained face down and sedated.

The transfer was ordered after the mentally ill inmate, who had insulin-dependant diabetes, refused to stop eating crackers and became aggressive.

The move was decided after a nurse expressed concern the crackers could worsen his already elevated blood sugar levels — but there is a dispute over who ordered it.

David Dungay was farewelled by family at a service in Kempsey in January 2016. ( Supplied: Dungay family with permission )

The senior officer in ward G, who's been given the pseudonym of "F", said he called in the Immediate Action Team (IAT) to handle the move because medical staff had ordered it.

"I wouldn't have moved him if the nurse didn't say that, would I?" he told the inquiry.

He denied he called in the IAT without permission from medical staff, and against protocol, despite agreeing the situation constituted neither a security nor medical emergency.

Officer "F" said it never occurred to him to brief the IAT to enter Mr Dungay's cell and remove the biscuits.

The opening day of the inquest was shown harrowing video footage of Mr Dungay's final moments.

Guards questioned breathing complaint

During the operation Mr Dungay was spitting blood from an injury and yelled repeatedly that he couldn't breathe.

Officer "F" said he thought the complaint was a ruse when Mr Dungay was in the first cell, that it might be true when he was between cells, and then a ruse again in the second cell.

He said he could see Mr Dungay's chest moving from the door of the second cell and hear him breathing, even though IAT officers had the inmate's chest pinned flat to the bed and his head turned to the wall.

Officer "F" told the inquiry he eventually became concerned that Mr Dungay really was having breathing difficulties, but he did not seek medical help or inform the IAT officers.

In earlier evidence, Officer F's subordinate, Officer "E", questioned the ability of medical staff to deal with aggressive inmates.

Officer E said the thought of getting medical staff to try to calm Mr Dungay hadn't crossed his mind.

He said corrective officers did a better job of dealing with aggression.

"I've seen doctors and nurses inflame the situation," he told the hearing.