A man claiming to be the driver posted an emotional statement on Facebook, saying he was drunk at the time and did not want to drive in the first place.
He said he was "so sorry, guys'' and needed time to cope with what he had done, as he did not know until afterwards that someone had died.
"I must pay,'' he said.
It is understood the driver had been at large after the accident happened late on Friday night.
Police confirmed this afternoon that a man was assisting officers in relation to this case.
A spokeswoman said police were not looking for anyone else.
The 18-year-old passenger who died in the crash has been identified as Alexia Noble-Hazelwood.
Three people were also injured in the crash and taken to hospital for treatment.
Emergency services were called to Gloucester St, in Christchurch, at 11.15pm after being alerted.
The vehicle involved had earlier been pursued by police. However, the pursuit was abandoned just minutes before the accident, police said.
Family and friends of Alexia have paid tribute to "our beautiful angel'' and have set up a Givealittle page to help her family pay for her funeral.
In a family notice published today, the Noble-Hazelwood family paid tribute to a beloved daughter to Angela and Denis and cherished sister to Kandie, Darson, Sharn, Shila and her twin brother Zackery.
Alexia's funeral will be held in Upper Riccarton on Thursday.
