Roads are melting around the country as the brutal summer heat takes its toll.

The New Zealand Transport Agency (NZTA) is taking drastic action, spraying down road surfaces to cool them down.

"Due to high temperatures today and high traffic volume the road surface on State Highway 1 (northbound) near the Johnstone Hill tunnel has reacted," the NZTA says on Facebook.

"Water trucks have been deployed to douse the road surface and dampening will continue until temperatures start to drop this evening.

"Dampening the road will reduce the stickiness and will allow traffic to return to normal peak flow. Please note a fresh bitumen seal was recently sprayed on this road. Motorists are advised to take care in the area and be prepared for some delays."