A serious two-car crash in Massey near Auckland's Northwestern Motorway is causing delays.

One person has been seriously hurt in the crash, on Triangle Rd about 6.30am, while another received moderate injuries, police said.

St John said it had taken two patients to Auckland Hospital.

Triangle Rd is partially blocked between Waimumu Rd and Lincoln Rd as serious crash investigators examine the scene.

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However, traffic is moving slowly along the road in both directions, Auckland Transport said.

"Please avoid this route if possible or expect delays," it said.