Motorists are being warned to expect delays after a truck crashed off a Wellington highway leaving a lane blocked.

Emergency services are at the scene near the Haywards Interchange on SH2 after the truck left the road.

The southbound lane is currently closed and long queues are starting to form.

Traffic is moving at a snail's pace through the gridlocked section of motorway.

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Police said the accident happened around 1km south of the interchange.

Those heading into the city should expect delays and take alternative routes where possible.