One person is seriously injured and traffic is backed up for several kilometres after a crash on State Highway 1 northbound at Conifer Grove, south of Manurewa, this afternoon.

Police said in a statement they were called to a “serious two-vehicle crash” near Conifer Grove about 12.30pm on Saturday where initial indications were one person was seriously injured.

The Herald understands a motorcycle was involved.

The motorway is closed northbound after the crash and traffic diversions are in place. Police said motorists should avoid the area and take an alternative route.

NZTA said via a social media post: “SH1 northbound between the Takanini off and on-ramp remain closed while police investigate the prior crash. A diversion has been put in place however consider delaying your journey or using an alternate route.”

Google Maps data showed traffic backed up for more than 5km on the northbound lane of the Southern Motorway as of 1.30pm.