Auckland Transport said bus route 394 was detoured.
“All bus stops on Paerāta Rd between Heights and Glenbrook Drive, as well as all stops on Jonah Lomu Drive missed, due to detour,” the agency reported on social media.
Fire and Emergency New Zealand (Fenz) said in statement that two fire trucks were at the scene. Crews with rescue gear are working to free one “partially trapped” person.
Earlier, a nearby three-vehicle crash blocked a lane on the southern motorway.
Police said the crash on State Highway 1 near Ramarama occurred at 5.30am. A lane was blocked for nearly two hours but has since reopened.
There were no serious injuries.