Part of Auckland's Southern Motorway northbound is down to one lane after a van rolled this evening.

Northern Police Communications Shift Inspector Chris Robinson said three people were injured, one in a serious condition.

The crash occurred north of the Newmarket Viaduct around 7pm, NZTA reported.

Motorists were advised to take extra care, avoid the area if possible, or delay travel.

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Detours could be taken via Market Rd or by using the Greenlane exit.

The SH1 Gillies Ave on-ramp northbound was also closed as a result.

Northbound motorists would need to enter the motorway at Hobson St, Wellington St or Shelley Beach Rd.

The motorway was not expected to be cleared till about 8.30pm. The police serious crash unit was in attendance.