Two crashes Auckland's Southwestern Motorway - including a car which came off a transporter - have caused delays on the network.

Emergency services were first called to a section of State Highway 20 near Puhinui Rd.

Traffic camera footage shows a car on its roof - with debris strewn around it - as a line of vehicles slowly pass it. The incident happened about 9.30am.

The NZ Transport Agency said: "A lost load from a vehicle-carrier is blocking the left lane, northbound, after Puhinui Road. Merge right with care to pass and expect delays until cleared.''

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It is not yet known whether anyone is injured.

Northbound lanes were opened eventually before 11am.

But another crash shortly afterwards led to the blockage of the northbound lane after the Lambie Dr off-ramp.

NZTA warned motorists of delays.