Update, 4.45pm: State Highway 2 through the Karangahake Gorge has reopened following an earlier crash involving a motorcycle.

A SunLive reader who is travelling from Tauranga to Auckland says that traffic is now flowing again in both directions.

"They've just reopened it,' says the motorist.

Update, 4.30pm: A motorist at the scene of a crash at Karangahake Gorge says that traffic management is diverting all northbound traffic to State Highway 25 towards Whangamata.

"In the past 30 minutes, traffic management have allowed southbound vehicles through State Highway 2," says the motorist.

"And we've just received an alert from traffic management that the northbound lane may be opening within half an hour."

Emergency services were notified of the serious crash involving a motorcycle just after 1pm.

One person is reportedly seriously injured and the road has been blocked wtih motorists advised to avoid the area or delay their journey.

Google Maps live traffic showing heavy congestion in Karangahake Gorge. Photo: Google Maps.

Update 3.30pm: A motorist heading towards Auckland from Tauranga has told SunLive that SH2 is still blocked, and traffic management expects the road to remain closed for a few more hours.

"Traffic management are diverting all vehicles towards Waitawheta Road and the road that leads to Whangamata," says the motorist.

"Traffic management has told me it's going to take a couple of hours to reopen the road. I'm travelling from Tauranga to Auckland so I'll just have to wait here until it opens again."

The diversion, according to the motorist. Photo: Google Maps.

A rescue helicopter arriving at the scene in the karangahake Gorge. Photo: Patricia Rushton.

Earlier, 1.49pm:

Emergency services are attending a serious crash involving a motorbike on State Highway 2, Karangahake.

"Due to a serious crash near Rahu Rd, Karangahake Gorge, the road is blocked. Allow extra time for detour," says a NZ Transport Agency spokesperson.

Southbound traffic from Paeroa is being advised to use use SH26, SH25A, SH25 to SH2 Waihi.

Northbound traffic from Waihi is being advised to use SH25, SH25A, SH26 to SH2 Paeroa.

A police spokesperson says they were notified of the crash just after 1pm.

"One person is reportedly seriously injured," says the spokesperson.

"The road is blocked and motorists are asked to avoid the area."

SunLive is working on providing an update as soon as possible.

At the scene? Phone 0800 SUNLIVE or email newsroom@thesun.co.nz