The Manawatu Gorge Road could be closed for up to a week because of a large slip.
The landslide containing about 1000 cubic metres of soil and debris came down about 9pm on Thursday, 2km from the Ashhurst end of the gorge on State Highway 3.
Transport Agency regional state highways manager David McGonigal said debris was still coming down on Friday and the area was very unstable.
Motorists can use the Pahiatua Track and Saddle Road as alternatives.
Meanwhile State Highway 1, the Desert Road, has reopened after being closed because of ice.