Two people have been choppered to hospital after a boat capsized on the Eyre River, west of Kaiapoi.
Emergency services were called to the shores of the river, which flows south-east into the Waimakariri River, shortly before 3pm after the boat carrying the group of four toppled.
Two of the four-strong group were injured in the incident, one seriously and one moderately.
A rescue chopper has flown the pair to Christchurch Hospital, a St John spokeswoman says.
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The other two in the party did not require medical assessment or treatment, she said.
Two fire trucks from the Kaiapoi brigade were at the river shore trying to get access to the party, Fire and Emergency New Zealand southern shift manager Lyn Crossan said.
It's the second water incident in the area in a week, after a person died in a boat-related incident in Kaiapoi last Wednesday.
Police were called to the Waimakariri River around 7.30am and the boat was found a short time later.
A spokeswoman confirmed it was not a drowning incident.