One of the critical patients was transported by helicopter to Waikato Hospital, the spokesperson said.
The other two critically injured patients and the person in serious condition were taken to hospital via road, St John said.
The road was initially closed and cordons erected at the intersection of SH26 and Schollum Rd and SH26 and Kuranui Rd.
The road has since reopened.
Motorists were asked to avoid the area and expect delays.
A couple of hours south, a collision between a truck and a car in Reporoa has left one person injured.
Emergency services are in attendance and the person is being airlifted to Waikato Hospital in serious condition, Police said in a statement.
The crash occurred at the intersection of Broadlands Rd and Butchers Pool Rd, Reporoa.
The collision was reported to police just after 8pm.
The road is blocked and diversions are being put in place, a police spokesperson said.
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