A 40-year-old pregnant woman critically injured in a car crash on Friday is now in a serious condition in hospital.

The woman was one of three people taken to Auckland City Hospital following the crash in Dome Valley.

She was originally in a critical condition.

The other two people are in a stable condition, a hospital spokeswoman said.

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The three people were trapped in their vehicles after the crash and had to be freed by fire crews.

The pregnant woman was the driver of one of the vehicles.

The crash closed State Highway 1 between Wellsford and Warkworth for nearly four hours.