A crash on Auckland's Harbour Bridge and another on the Southern Motorway have caused issues for motorists heading north this evening.

Just before 5pm the NZTA said a crash was blocking the northbound left-hand lane on the Harbour Bridge. The crash has now been cleared but traffic is backed up.

Earlier three trucks and one car were involved in a crash near the Southern Motorway's Khyber Pass exit shortly before 3pm.

Police said no one was injured in the "minor nose to tail crash", which happened on the northbound side between the Gillies Ave and Khyber Pass off-ramps.

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The accident caused traffic to build in the area - just in time for after-school traffic.

All lanes were reopened by 4pm but police were warning motorists to expect delays, with traffic still heavy from Mt Wellington to Newmarket.

At 3pm the NZTA's live traffic map shows congestion backed up from as far north as Freemans Bay and as far south as Greenlane.