Motorists are being told to expect delays after a series of crashes as intense rain pelted Auckland.

Forcaster Weatherwatch says slow-moving rain bands are crossing the upper North Island, bringing rain heavy enough to cause flooding of roads, gutters and basements to Northland, Auckland, Waikato and Coromandel Peninsula.

A crash on the Southern Motorway blocked the northbound lane just after the Razorback Rd overbridge.

It has been cleared but New Zealand Transport warned of delays as congestion eases.

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Earlier, a truck broke down on State Highway 1 at Puhoi.

It blocked the northbound lane near Schollum Access Rd.

"Expect delays and take extra care when passing through the area," NZTA tweeted.

Two vehicles have also crashed at the intersection of Whitford-Maraetai Rd and Henson Rd in Whitford.

The crash, which happened around 3.25pm, left one person trapped in their vehicle and needing to be freed by firefighters. Their injuries are believed to be minor.

Meanwhile emergency services are cleaning up Takanini Rd after used needles were dumped.

Fire and Emergency New Zealand (FENZ) shift manager Craig Dally said one crew was at the site of the drop, after St John Ambulance requested help in the clean-up.

Fenz were notified of the littering on Great South Rd/Walters Rd, just after the roundabout, at 2.42pm this afternoon, Dally said.

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One truck with four crew members was sent to help pick up the numerous needles.

A bystander told the Herald that the Fenz crew at the scene requested WorkSafe to be notified of the event.

A St John Spokesperson directed inquiries to police.

A police spokesman said officers were initally at the scene, but have since left.