Two mates who had been drinking at a Christmas function in Christchurch crashed on the same road about 30 seconds apart on Thursday night.
One of the vehicles flipped and landed upside down in a water race on Lincoln Tai Tapu Rd, Rolleston, about 10pm. The other vehicle also ran off the road and landed in a dry ditch.
Senior Constable Andy Williamson said the upside-down was lucky to survive: "I don't know how the hell he got out. He was lucky he wasn't killed."
Both drivers were out of their vehicles when emergency services arrived.
When police tested them for alcohol, one recorded more than 900mcg of alcohol per litre of breath - and the other more than 500mcg, Williamson said. Both drivers are under the age of 20.