Only one lane is open through the Karangahake Gorge because a truck has broken down and blocked the other.
It's expected the gorge will be down to one lane until about 5pm, police said in a statement.
Motorists are being asked to delay travel through the gorge between Paeroa and Waihi.
Traffic management had been put in place.
Waka Kotahi NZ Transport Agency said on Twitter the incident had taken place east of School Rd.
