Three people have been injured in a two-car crash on State Highway One near Ashburton.
Emergency services were called to the crash at about 11am.
A St John spokesperson said three people were injured, one moderately and two seriously.
The two people in a serious condition are being airlifted to Christchurch Hospital.
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Three ambulances, one first response unit and two helicopters responded, they said.
The highway was closed but reopened at about 2pm. Motorists are advised to expect delays.
An NZME reporter at the scene said traffic had backed up and it was taking about 45 minutes to get through Ashburton at about 2pm.
A Fire and Emergency NZ spokesman said two people were trapped in one vehicle but had been freed by 12.20pm.
An NZTA spokesperson said traffic is starting to back up considerably at the crash site.
"Expect delays & please follow the direction of emergency services until this is clear."