UPDATED 6:59PM: Traffic is now flowing following a two vehicle crash south of Katikati this afternoon.
Emergency services were called to the crash on State Highway 2 just before 3.30pm.
The crash forced police to close the highway, which was later re-opened just after 5pm.
Police say two people were injured in the crash and both occupants, one from each vehicle, sustained serious injuries.
The cause of the crash is under investigation.
A caller to the 0800 SUNLIVE news hotline says traffic is now flowing as they make their way through Katikati, heading towards Tauranga.
Police re-opened SH2 near Rea Road Katikati to one lane about 5pm, and to two lanes about 20 minutes later, but are advising people to avoid using the road for some time because of the significant traffic backlog.
Two cars collided on a straight section of road near the Rereatukahia Stream bridge about 3.15pm.
Two people were trapped in each of the cars involved. Both are injured but police say they are not life threatening.
Traffic remains backed up for a considerable distance. Western Bay of Plenty road policing manager Senior Sergeant Ian Campion advises people to delay their journey because of the significant backlogs.
Travellers say traffic is backed up North of Katikati to Kauri Point and south as far as Aongatete.
The New Zealand Transport Agency advises people to divert through State Highway 29 Kaimai Ranges.
Motorists heading to the Bay of Plenty can turn off at Paeroa and use State Highway 26, State Highway 27 then State Highway 24 to reach State Highway 29.
The diversion could add an extra 45 minutes to a normal journey.
Road users are asked to avoid the area or delay all non-essential travel.