A police spokesperson said earlier five people were involved.
Two St John vehicles attended the incident and transported four people to Waikato Hospital.
Of the five people, St John said three had serious injuries, one person was moderately injured and a fifth person did not sustain any injuries.
The road from Te Kumi Station Rd to Lawrence St is currently closed with diversions in place while emergency services are in attendance.
The Serious Crash Unit has been advised and will be attending the scene and motorists should expect delays.
Meanwhile, one person has been critically injured following a single vehicle crash in Waikato.
Just after 6.30pm, police were notified about a car that had collided with a tree on Waterworks Rd in Te Miro.
The sole occupant has been transported to hospital via helicopter with critical injuries.
The road is closed and diversions are in place at Chepmell Rd and Te Miro Rd.