Key Points:

Speedway New Zealand has launched an investigation after a speedway driver died during a race at Western Springs in Auckland last night.

Shane Turner, 50, was believed to have suffered a heart attack or stroke before crashing into the barrier.

A man who saw the race and wished to remain anonymous told Mr Turner's head slumped against the wheel before his car collided at speed with the wall and turned over.

Mr Turner's wife and son were called to the speedway and despite efforts from medical staff, he was not revived.

The man said drivers would fly black ribbons from their cars at the next speedway meet in honour of Mr Turner who had been involved with the speedway for "umpteen years".

Speedway promoter Dave Stuart said the car was approaching a corner when it slowed down and crashed into a wall.

"When the crash crew got there, there was no response at all from the driver, which was really strange from their point of view for such a slow speed accident which didn't involve another car and the car didn't get upside down," he told

The race was stopped after the death.

Mr Stuart said Speedway New Zealand was looking into the death and talking to Mr Turner's family about how his life would be commemorated.