A witness has described how a speeding SUV was weaving between traffic shortly before losing control and flipping in a fatal crash on one of Auckland's busiest inner-city motorways. 

One person was killed following the crash on Auckland's Southern Motorway near Gillies Ave in Epsom on Thursday night. The crash led to major motorway congestion. 

A police spokesperson said a second person was taken to hospital with serious injuries after emergency services were alerted to the "multi-vehicle" crash about 8.10pm. 

A witness told the Herald a SUV was being driven dangerously and at high speed, swerving between lanes. 

"They were behind our car, then passed us and two other cars in front, before losing control and crashing against the wall on the side of the road and flipping several times. 

"Everything was very fast, we were very close, but fortunately avoided the crash. We saw the sparks from the collision against the concrete," the witness said. 

Police said the southbound lanes were closed, with traffic needing to exit at Gillies Ave and detouring through to the Greenlane on-ramp. 

The crash caused major motorway congestion, with reports of some motorists travelling just 100m in 40 minutes. 

The motorway reopened overnight. Police are investigating the crash. 

-More to come