A two-car crash in Auckland has injured two people and blocked a road, causing a diversion on to a state highway.

A police spokeswoman said they were called to the crash at 4.45pm on Old North Rd in Kumeu.

One person has serious injuries, and was being assessed by an ambulance, she said.

A second person had moderate injuries, she said.

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The crash occurred between Old Railway Rd and Riverhead Rd, she said.

"The road is blocked and diversions are in place."

The diversion would be the intersection of Old North Rd and State Highway 16, she said.

Auckland Transport says a section of Old North Rd in Kumeu is closed and urged motorists to follow the directions of emergency services for diversions.