A person is seriously injured after a crash on Auckland's southern motorway in Ellerslie. 

Two northbound lanes have been closed, which is affecting traffic. 

Police said the crash between a car and a motorbike happened at 1.45pm in the northbound lanes. 

"Emergency services are in attendance at a serious crash on Auckland's southern motorway in Ellerslie," police said in a statement. 

"One person has sustained serious injuries." 

Emergency services are at the scene and the Serious Crash Unit has been advised.