The scrub fire is just behind theme park Rainbow's End.
However, it was not thought there was any danger to nearby buildings or properties, the Fire Service said.
Motorist Abdul Rahman said he was driving towards Manukau, from the city, when he saw large plumes of smoke heading towards him.
"The wind was spreading the smoke towards the motorway and motorists started to slow down because you couldn't see the road properly.''
He said he and his wife decided to turn into the Redoubt Rd on-ramp to wait a while.
Police are also at the scene and are expected to help with traffic control.
It is understood part of the motorway will be closed off as firefighters work to control the blaze.
The Fire Service said about 9.30pm that the blaze was under control but two trucks remained at the scene still.