The woman who fell from a moving campervan on the Waikato Expressway on Thursday remains in a critical condition.

The 59-year-old remains in Waikato Hospital's Intensive Care Unit after she was hurt trying to close a door when the wind blew it open and caused her to fall.

Waikato police Senior Seargeant Rupert Friend said a couple were travelling south on State Highway 1 when the woman sustained her injuries.

"A female passenger in a caravan has tried to fix a door that wasn't quite closed properly and has ended up being injured as a result of those activities," he said.

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The woman's husband was driving at the time.

She suffered significant grazing and cuts as she skidded along the highway.

Friend insisted that motorists pull over before attempting to check their vehicles as they drive along.

"I think the biggest thing is if you think there's anything wrong with your vehicle make sure you stop at the location before having a look at it or attempting to fix it," he said.

The Serious Crash Unit attended the scene but he didn't believe there was anything wrong with the vehicle.

Swerving skid marks were all that was left at the scene after the campervan was taken away.