An investigator checks the wreckage of one of the planes involved in the mid-air collision. Marty Melville / Getty Images

An investigator checks the wreckage of one of the planes involved in the mid-air collision. Marty Melville / Getty Images

One of two light aircraft which collided over Manawatu yesterday, killing both their pilots, had a close call with a rescue helicopter minutes earlier.

The two young male flyers, both mid-term students of Massey University's School of Aviation, were found dead in their cockpits after their single-engine Piper Cherokee training craft crashed into paddocks near Shannon, southwest of Palmerston North, about 10am.

The men killed were Brandon James Gedge, 20, from Tauranga, and Dae Jin Hwang, 27, from West Auckland.

Farmers who watched the tragedy unfold said the aircraft had been flying overhead for up to 15 minutes, conducting stalling manoeuvres before the wing of one of the Cherokees clipped the tail of the other.

Rodney Hudson, into whose dairy farm the planes plummeted off Ngui Rd north of Shannon, said he saw the southbound rescue helicopter climb and turn to avoid a collision with one of the aircraft several minutes before the crash.

The two training planes were flying "reasonably close together for a period of time".

The pilot of a topdressing aircraft also in the area described on television seeing the wreckage on the ground and then looking up to see debris floating to the ground like "confetti" out of a clear blue sky.

A spokesman for the Palmerston North-based Square Trust rescue helicopter confirmed to the Herald last night that it was forced to take evasive action after a northbound Cherokee turned into its path.

What ensued minutes later was New Zealand's first fatal mid-air collision since the police Eagle helicopter and a fixed-wing traffic-spotting aircraft collided over Auckland's central motorway junction in 1993, killing four people.

It is not the first time tragedy has struck the Massey aviation school, which lost a student in an air crash in the Ureweras during a navigational exercise in 1995.

Wreckage of his aircraft, which was supposed to have been flying between Gisborne and Palmerston North, was not found for several years.

Civil Aviation Authority spokesman Bill Sommer, whose agency is investigating the latest accident, said it was "obviously a high-impact crash - it was not a little nudge".

The aircraft appeared from their transponders to have collided at right angles, one while climbing on a northbound path and the other descending to the east.

He said it was possible that the pilots, both bachelor of aviation students with more than 100 flying hours under their belts, might not have seen what was in store for them.