A woman has been critically injured after she was hit by a train north of Wellington today.

The woman, aged between 30 and 40, was hit opposite Whitford Brown Avenue at Porirua, about 11.15am, police said.

State Highway 1 was briefly closed for a helicopter to land, but the woman was taken to Wellington Hospital by ambulance.

A KiwiRail spokeswoman said the line had closed between Waikanae and Porirua and a bus service was running, while police checked the scene.