It was a St John communications staff member, asking him to go back to work urgently as an incident was unfolding.
At the ambulance station, he and another station officer were told there had been a house fire and a shooting in Aramoana.
Flett drove the second ambulance that was sent to the scene.
He remembered the ambulance being quickly overtaken in the winding Aramoana Rd by two police cars containing members of the Armed Offenders Squad.
He parked the ambulance at a safe arrival point set up near a row of cribs near the entrance to the settlement.
By that point, the first ambulance had already picked up one victim.
He did not know how serious the situation was.
"We could see smoke, from the house fire. We didn't know numbers at that stage."
Then the gunfire started.
He later learned that was David Gray shooting at police officers who had gone in to rescue Chris Cole, who had been shot.
They were quickly told to relocate to nearby Te Ngaru.
"When the shooting started, the whole mood just changed. You know, 'this is for real'."
Then a police van came screaming up the road, a door half hanging off.
Inside were two officers and the injured Cole, lying across their knees.
The ambulance staff quickly got him on to a stretcher, discovering he was conscious but badly wounded.
He would later die in hospital.
Flett had been in the job for six years at that point, and had never seen anything like it.
Thirty years on, even after responding to events such as the Christchurch earthquakes, it still stands out.
"It was very, very tragic thing that happened."
He thought it would never happen in New Zealand again — until the Christchurch terror attack.
The gun legislation passed as a result was long overdue, he said.
"It was just a no-brainer."
