State Highway 36 between Tauranga and Rotorua is to remain closed for two weeks longer than originally planned to allow for further safety works following a rock fall in August.
The Transport Agency says the extended closure will allow contractors to complete bolting and netting of the rock face in the Mangorewa Gorge.
It had been hoped the highway would reopen on Monday. However, the agency says the safety of motorists and workmen is the top priority.
The new target date is 28 September.
The Department of Labour and GNS Science are investigating the cause of the rock fall which crushed a moving car on 6 August.