UPDATE 12.51pm: SH29 Lower Kaimai Range is now open, according to a police spokesperson.

"One person has been transported to Waikato Hospital with serious injuries following a crash on SH29, Lower Kaimai Range, reported at 8am," says the spokesperson.

"An investigation to the crash remains ongoing."

A video supplied to SunLive shows the heavily congested traffic building up after the crash.

EARLIER 12.42pm: SH29, Lower Kaimai Range is now open to eastbound traffic following a serious crash, but remains closed to westbound traffic, according to a Waka Kotahi NZTA spokesperson.

"No detour required for eastbound traffic. Westbound left to Omanawa Road, right to Peers Road, right to McLaren Falls Road, left to return to SH29. This detour is not suitable for HPMV."

The spokesperson adds the incident is between Omanawa Road and McLaren Falls Road.

EARLIER 12.04pm: Two people have been injured following a serious crash on State Highway 29.

Emergency services were called to the crash, involving two vehicles, just before 8am.

A St John spokesperson says two ambulances, a helicopter and two rapid response vehicles responded to the crash.

'Two patients were assessed at the scene

'One person was in critical condition and transported to Waikato Hospital by helicopter and one person was in moderate condition and transported to Tauranga Hospital by road ambulance.”

A police spokesperson says the highway, between Poripori and Thorne roads, remains closed.

'The road will remain closed while Serious Crash Unit conduct a scene investigation.”

A video sent to SunLive by a woman travelling to Cambridge via State Highway 29 shows just how back-up the traffic is.

Diversions are in place and motorists are advised to avoid the area if possible.

Meanwhile, traffic delays are being reported in SH2, through the Karangahake Gorge.

A truck has broken down and is blocking one lane east of School Road.

Stop/go traffic management is currently in place.