Police are investigating the incident on behalf of the coroner.
A police spokeswoman said they were currently briefing Safe Air about their investigation.
A spokesman for the Department of Labour said it had launched its own investigation, with two local staff working on it.
The department's investigation could take up to six months, he said.
Air NZ said the Rolls Royce C-130 Hercules turboprop engine was being tested without its propellers on a remote stand at the time of the incident.
A turboprop engine is a combination of a jet engine with a propeller on the front, an Air NZ spokeswoman told NZPA.
Air NZ would co-operate with both investigations, she said.
A former employee told the Marlborough Express, Safe Air tested Hercules engines on a frame in a remote corner of the airport once they had been serviced.
The man was thought to have entered the testing enclosure while the engine was running.
A source told the paper the engine had been taken into a Air Force hangar to be dismantled to recover the body.
Police said the man would not be named until next of kin were notified.
Air NZ chief executive Rob Fyfe earlier arrived in Blenheim to support the engineer's family, friends and colleagues.
The Engineering, Printing and Manufacturing Union confirmed the dead man was a member of the union and expressed its condolences to his family.
- NZPA
