Emergency services were called to Joy St in Shirley at 3.25pm after reports of an assault.
A police spokesperson said a person received serious injuries and was taken to Christchurch Hospital.
"I can confirm two youths were located and taken into custody in relation to the assault on Joy Street," police said.
St John responded with an ambulance and two rapid response vehicles.
A commercial helicopter was called in to help police find a vehicle linked to the assault, which was spotted in the Avonside and Dallington areas.
One of the youths was arrested in Wainoni after being handed over to police by his mother, chrislynchmedia.com reported.
Superintendent Lane Todd said during their investigation six young people were also arrested for unrelated matters.
They were charged with unlawfully taking motor vehicles and burglary, and were due to appear in Youth Court at a later date.
"This behaviour is unacceptable and will not be tolerated, anyone who chooses to engage in this behaviour can expect to be held to account," Todd said.
