A Palmerston North man killed while trying to evade police was driving at speed without his lights on and swerved to avoid another motorist when he lost control of his car, a coroner has found.

Jason Luke Downes, 25, unemployed, died from head injuries when his car crashed into a ditch on Palmerston North's Pioneer Highway about 11.30pm on May 4.

The crash happened while Mr Downes was being followed by a police officer, who clocked him racing another car at 128km/h in a 50km/h zone and followed the drivers.

However, Palmerston North coroner Tim Scott did not find Constable Rob Illingworth responsible for the accident, the Manawatu Standard reported.

It was not a regulation pursuit, as he turned off the police lights after the racing drivers turned their headlights off, although Mr Illingworth did drive over the speed limit, Mr Scott said.

When a woman pulled her car out from a side road into Mr Downes' path, unable to see the unlit vehicles travelling at speed, Mr Downes swerved and his car left the road, landing into a water-filled ditch.

There was no alcohol in Mr Downes' blood, and the small amount of cannabis was not enough to affect his driving, Mr Scott said.

Neither man was wearing a seatbelt.