A milk tanker and two cars have crashed off SH1 near St Andrews in Canterbury.
Two people were trapped, one in each car, a Fire Service shift manager said.
Three fire crews are attending, as well as police and ambulance.
Firefighters were "currently extricating" one person and would be assisting with the second person after that.
A St John spokesman said one patient was in a serious condition while the other had moderate injuries.
Both have been taken to Timaru Hospital.
The crash happened shortly before 6pm.