A police spokesperson told Chris Lynch Media emergency services were called to Radley Street, near Ferry Road, just after 1 pm.
One of the vehicles ended up in the Heathcote River.
The eyewitness said he was travelling towards town when he saw one of the vehicles go through an orange light on Ferry Road.
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“He kept going through it, and a car turning onto Radley Street went to turn and collided with the vehicle.
“My mate and I jumped straight out, ran down the bank, pulled open the back door of the vehicle, and helped the man, in his 80s, back up to the footpath.
“Within 10 minutes, emergency services had arrived. The car was half submerged in water.”
A St John spokesperson said they responded with one ambulance and one rapid response vehicle. Two patients were assessed, and one was transported to Christchurch Hospital in moderate condition.
