Motorists are being warned of surface flooding on the highway through Karangahake Gorge.

"Due to surface flooding on SH2 between Paeroa and Waihi, caution is advised along this route," says a Waka Kotahi NZTA spokesperson.

Michael Small of Paeroa Towing Services says traffic is moving slowly through the gorge on Monday morning.

"It's pretty much bumper to bumper, stop start." says Michael.